diff --git a/custom_components/localthings/registry/by_type/air_purifier.py b/custom_components/localthings/registry/by_type/air_purifier.py
index ca67d32..605b2a4 100644
--- a/custom_components/localthings/registry/by_type/air_purifier.py
+++ b/custom_components/localthings/registry/by_type/air_purifier.py
@@ -22,6 +22,12 @@ match_fn discriminators that keep them from colliding):
   resource surface as A-VTWW-TP2-21-COMMON above; no new capabilities
   needed.
 
+AIR_LEVEL_CHECK ("AI Purify" -- the periodic air-quality sensing engine on
+/airlevelcheck/vs/0) is shared by the last three of those: their dumps all
+carry the resource with the same field names, and only the TVTL family has no
+such href. It was covered as opaque plumbing until two AVT-WW-TP1 dumps
+(issues #84 and #190) showed it drives a real user-facing feature.
+
 Reuses dishwasher.DIAGNOSIS for /diagnosis/vs/0 (identical field/write
 contract).
 """
@@ -38,6 +44,7 @@ REGISTRY = DeviceRegistry(
             *common.POWER,
             dishwasher.DIAGNOSIS,
             air_purifier.AIR_QUALITY,
+            air_purifier.AIR_LEVEL_CHECK,
             air_purifier.FILTER,
             air_purifier.DEVICE_ACTIVE,
             air_purifier.AIRFLOW_GENERIC,
diff --git a/custom_components/localthings/registry/capabilities/air_purifier.py b/custom_components/localthings/registry/capabilities/air_purifier.py
index 5b86e91..887b6be 100644
--- a/custom_components/localthings/registry/capabilities/air_purifier.py
+++ b/custom_components/localthings/registry/capabilities/air_purifier.py
@@ -58,6 +58,8 @@ one unit, stuck at 0 throughout on the other), so AIRFLOW_VS_FALLBACK below
 stays a plain read-only diagnostic even after this change.
 """
 
+import datetime
+
 from ..capability import Capability
 from ..entities import (
     BinarySensorDesc,
@@ -66,8 +68,9 @@ from ..entities import (
     SelectDesc,
     SensorDesc,
     SwitchDesc,
+    TimeDesc,
 )
-from .common import filter_usage_percent, int_or_none, sensor_item_value
+from .common import epoch_to_utc, filter_usage_percent, int_or_none, sensor_item_value
 from .laundry import bool_option_exists, bool_option_value, option_value, option_write
 
 # Newer TP1X_DA-AC-AIR-class boards (e.g. TP1X_DA-AC-AIR-01031_0000, issue
@@ -507,6 +510,266 @@ SOUND_VOLUME = Capability(
     ),
 )
 
+# ---------------------------------------------------------------------------
+# AI Purify -- /airlevelcheck/vs/0 (issues #84 and #190)
+#
+# Covered as "periodic air-quality sensing scheduler plumbing" until two dumps
+# of the AVT-WW-TP1-23 board showed it is not plumbing: it drives the feature
+# the SmartThings app calls AI Purify, where the unit wakes on a timer, samples
+# the air, and optionally acts on the result. Every field is named, none are
+# opaque, and two of them are already user-set on the reported units.
+#
+# Three of this registry's four board families report the resource with the
+# same field names -- TP1X_DA-AC-AIR (#130), A-VTWW-TP2 (#151) and AVT-WW-TP1
+# (#84, #190); only ARTIK051_TVTL (#56) has no such href. Bound unconditionally
+# rather than behind a match_fn so any board reporting it is covered; the one
+# field that genuinely varies is gated per-entity below.
+#
+# The resource carries two independent knobs and they get one entity each,
+# rather than being folded into a single control:
+#
+#   periodicSensingActivationState  On/Off              -- is AI Purify running
+#   autoExeState                    Off/Airpurify/Alarm -- what it does with a
+#                                                          bad reading
+#
+# The appliance itself presents them that way: its own UI has an on/off for AI
+# Purify separately from the three mode choices. Folding them into one select
+# was tried first and lost two things -- a configured action became invisible
+# while the feature was off, and no option could toggle the feature without
+# also overwriting the action.
+#
+# Note the two 'off's mean opposite things and are not interchangeable. The
+# switch's off stops the unit sampling at all; the select's off is the
+# advertised autoExeState "Off", where the unit keeps sampling and simply
+# doesn't act on what it measures -- the app calls that choice "sensing only".
+#
+# The select reads its options straight off supportedAutoExeState rather than
+# a typed-in tuple, the same shape SOUND_MODE below uses for supportedModes: a
+# board advertising a fourth action gets it accepted on both the options list
+# and the write path.
+#
+# range_hood.AIR_LEVEL_CHECK already models this same href, and its read-only
+# keys (air_sensing_state / last_air_sensing_time / last_air_sensing_level) are
+# reused verbatim so both families share one catalog entry. It is deliberately
+# NOT imported: the hood exposes periodic_air_sensing as a read-only
+# BinarySensorDesc and this board needs a writable SwitchDesc on that same key,
+# so reusing the hood's capability would migrate every hood user's entity to a
+# different platform.
+#
+# Verification: every write below was exercised on AVT-WW-TP1-23-AXX500
+# hardware. This board returns 2.04 for writes it silently discards (see
+# HEPA_FILTER's filter-reset note), so an echo proves nothing -- each was
+# judged by the value surviving a reconnect, which forces a new DTLS session,
+# fresh discovery and a fresh observe of this href, leaving no cached state to
+# read back. The other two families get the writes on field-shape grounds, the
+# same basis on which they already share MODE, HEPA_FILTER and the air-quality
+# sensors.
+#
+# Deferred: startSensingOnce (On/Off on all three dumps) looks like a one-shot
+# "sense now" trigger and would be a ButtonDesc, but nothing here writes it yet
+# and this board is known to acknowledge writes it discards -- so it stays
+# unbound until someone can confirm the side effect rather than the echo.
+# ---------------------------------------------------------------------------
+
+
+def _interval_minutes(seconds):
+    """Device stores the interval in seconds; the entity is in minutes.
+
+    `is None` rather than a falsy check so a reported 0 is distinguishable
+    from a missing one. Anything else nonzero rounds up rather than to
+    nearest, so a sub-minute value can't render as 0 and fall below the
+    entity's own floor.
+    """
+    secs = int_or_none(seconds)
+    if secs is None:
+        return None
+    return -(-secs // 60) if secs > 0 else 0
+
+
+def _interval_write(payload, rep, href=None):
+    # Minutes in the UI -> seconds on the wire (scalar string). Modelled as a
+    # free Number rather than the app's three fixed choices (10 min / 30 min /
+    # 1 hour): this resource advertises no supported-values or range field for
+    # the interval -- supportedAutoExeState sits right beside it, so the board
+    # does advertise constraints where it has them -- and it accepts values the
+    # app never offers. Writing 60 s, six times finer than the app's smallest
+    # choice, drove an observed ~60 s sensing cycle on hardware.
+    #
+    # One minute is the floor because that's the resolution this board reports
+    # results at: lastSensingTime lands on an exact minute on every sample from
+    # the AVT-WW-TP1 and A-VTWW-TP2 boards (both fixtures, and eleven
+    # consecutive live readings), where the TP1X/AC/hood boards report arbitrary
+    # seconds. A sub-minute interval is therefore unobservable here whether or
+    # not the board honours it. Zero is refused for a separate reason: unlike
+    # oven.cook_time or operational's delay hours, where 0 is a real setting
+    # ("no timer", "no delay"), nothing establishes what a 0 interval does to
+    # this board -- so native_min stops the UI offering it, and this guard
+    # covers the service-call path. Silent no-op via a None return, the same
+    # shape range_hood._lamp_level_write uses for a level the device didn't
+    # advertise.
+    minutes = round(float(payload))
+    if minutes < 1:
+        return None
+    return ["airlevelcheck", "vs", "0"], {
+        "x.com.samsung.da.periodicSensingInterval": str(minutes * 60)
+    }
+
+
+def _periodic_sensing_write(payload, rep, href=None):
+    # The master on/off for AI Purify. Leaves autoExeState alone, so the
+    # configured action survives the feature being switched off and comes back
+    # with it -- the thing the select cannot do, since every option it writes
+    # sets an action.
+    return ["airlevelcheck", "vs", "0"], {
+        "x.com.samsung.da.periodicSensingActivationState": ("On" if payload == "On" else "Off")
+    }
+
+
+def _skip_status_write(payload, rep, href=None):
+    return ["airlevelcheck", "vs", "0"], {
+        "x.com.samsung.da.periodicSensingSkipStatus": ("On" if payload == "On" else "Off")
+    }
+
+
+# The daily window during which periodic sensing is skipped, stored as one
+# HHMMHHMM string (start+end) on periodicSensingSkipTime. The read side is
+# cross-confirmed on two units: issue #84's sits at the inert '00000000', while
+# issue #190's carries a real user-set '03002300' -> 03:00-23:00. Split into
+# two HA time entities; each write reads the other half back out of the live
+# rep so the pair round-trips. Confirmed in both directions on hardware: from
+# 13:00-23:00, writing start=07:30 then end=22:00 left the device holding
+# '07302200' -- each write kept the half it wasn't given.
+def _skip_time_read(part):
+    def _read(value):
+        raw = str(value or "")
+        chunk = raw[0:4] if part == "start" else raw[4:8]
+        if len(chunk) == 4 and chunk.isdigit():
+            try:
+                return datetime.time(int(chunk[:2]), int(chunk[2:]))
+            except ValueError:
+                return None
+        return None
+
+    return _read
+
+
+def _skip_half(raw, part):
+    """The half this write isn't setting, normalized. Padding alone would carry
+    a malformed value straight back to the device -- writing start over a junk
+    skip time would send '0730' + junk. The read side already refuses a half it
+    can't parse, so an unparseable one becomes '0000' here and the pair
+    round-trips honestly in the same cases."""
+    chunk = (str(raw or "") + "00000000")[:8]
+    other = chunk[4:8] if part == "start" else chunk[0:4]
+    return other if _skip_time_read("end" if part == "start" else "start")(chunk) else "0000"
+
+
+def _skip_time_write(part):
+    def _write(value, rep, href=None):
+        raw = rep.get("x.com.samsung.da.periodicSensingSkipTime", "")
+        hhmm = f"{value.hour:02d}{value.minute:02d}"
+        other = _skip_half(raw, part)
+        new = hhmm + other if part == "start" else other + hhmm
+        return ["airlevelcheck", "vs", "0"], {"x.com.samsung.da.periodicSensingSkipTime": new}
+
+    return _write
+
+
+AIR_LEVEL_CHECK = Capability(
+    href="/airlevelcheck/vs/0",
+    poll_tier="warm",
+    entities=(
+        SwitchDesc(
+            key="periodic_air_sensing",
+            field="x.com.samsung.da.periodicSensingActivationState",
+            icon="mdi:radar",
+            entity_category="config",
+            value_fn=lambda v: str(v).lower() == "on",
+            write_fn=_periodic_sensing_write,
+        ),
+        # Options come off supportedAutoExeState, not a table here -- the
+        # catalog carries the labels for the three values seen so far, and an
+        # unrecognized fourth still reaches the user (select.py falls back to
+        # the device's own token when the catalog doesn't know it).
+        SelectDesc(
+            key="sensing_mode",
+            field="x.com.samsung.da.autoExeState",
+            options_field="x.com.samsung.da.supportedAutoExeState",
+            translation_key="sensing_mode",
+            icon="mdi:radar",
+            entity_category="config",
+            write_fn=lambda p, rep, href=None: (
+                ["airlevelcheck", "vs", "0"],
+                {"x.com.samsung.da.autoExeState": p},
+            ),
+        ),
+        # The one field that varies across the three families reporting this
+        # resource: the TP1X_DA-AC-AIR dump (#130) omits it while both
+        # AVT-WW-TP1 dumps and the A-VTWW-TP2 dump carry it, so that board runs
+        # the sensing engine on a fixed interval it doesn't expose.
+        NumberDesc(
+            key="sensing_interval",
+            field="x.com.samsung.da.periodicSensingInterval",
+            icon="mdi:timer-cog",
+            entity_category="config",
+            native_min=1,
+            native_max=60,
+            step=1,
+            unit="min",
+            exists_fn=lambda rep, resources: "x.com.samsung.da.periodicSensingInterval" in rep,
+            value_fn=_interval_minutes,
+            write_fn=_interval_write,
+        ),
+        SwitchDesc(
+            key="periodic_sensing_skip_status",
+            field="x.com.samsung.da.periodicSensingSkipStatus",
+            icon="mdi:sleep",
+            entity_category="config",
+            value_fn=lambda v: str(v).lower() == "on",
+            write_fn=_skip_status_write,
+        ),
+        TimeDesc(
+            key="sensing_skip_start",
+            field="x.com.samsung.da.periodicSensingSkipTime",
+            icon="mdi:clock-start",
+            entity_category="config",
+            value_fn=_skip_time_read("start"),
+            write_fn=_skip_time_write("start"),
+        ),
+        TimeDesc(
+            key="sensing_skip_end",
+            field="x.com.samsung.da.periodicSensingSkipTime",
+            icon="mdi:clock-end",
+            entity_category="config",
+            value_fn=_skip_time_read("end"),
+            write_fn=_skip_time_write("end"),
+        ),
+        # Read-only status, same keys as range_hood.AIR_LEVEL_CHECK.
+        SensorDesc(
+            key="air_sensing_state",
+            field="x.com.samsung.da.sensingState",
+            icon="mdi:radar",
+            entity_category="diagnostic",
+        ),
+        SensorDesc(
+            key="last_air_sensing_time",
+            field="x.com.samsung.da.lastSensingTime",
+            device_class="timestamp",
+            entity_category="diagnostic",
+            value_fn=epoch_to_utc,
+        ),
+        # 'Kr1' on both dumps -- a national air-quality grade whose scale is
+        # region-prefixed and undocumented here, so it stays a raw diagnostic
+        # rather than being mapped to an asserted enum.
+        SensorDesc(
+            key="last_air_sensing_level",
+            field="x.com.samsung.da.lastSensingLevel",
+            icon="mdi:air-filter",
+            entity_category="diagnostic",
+        ),
+    ),
+)
+
 # /humidity/0 and /humidity/vs/0 are empty {} on both dumps this family has
 # been verified against -- covered here (not globally, per ignored.py's
 # module docstring) since those hrefs collide with fridge/AC schemas
@@ -522,7 +785,6 @@ SOUND_VOLUME = Capability(
 COVERAGE = [
     Capability(href="/humidity/0"),
     Capability(href="/humidity/vs/0"),
-    Capability(href="/airlevelcheck/vs/0"),  # periodic air-quality sensing scheduler plumbing
     Capability(href="/availablecontrolsets/vs/0"),  # opaque hex-encoded control-set bitmap
     Capability(href="/da/softreset/vs/0"),  # soft-reset trigger plumbing
     Capability(href="/keepnormalstate/vs/0"),  # internal keep-normal flag
diff --git a/custom_components/localthings/registry/capabilities/common.py b/custom_components/localthings/registry/capabilities/common.py
index b9e4855..fc78a02 100644
--- a/custom_components/localthings/registry/capabilities/common.py
+++ b/custom_components/localthings/registry/capabilities/common.py
@@ -64,6 +64,18 @@ def parse_iso_utc(raw):
     return dt if dt.tzinfo is not None else dt.replace(tzinfo=UTC)
 
 
+def epoch_to_utc(value):
+    """Unix epoch seconds -> aware UTC datetime, for the boards that report a
+    bare epoch rather than the ISO string parse_iso_utc handles. Lived in
+    range_hood.py as `_timestamp` until air_purifier.py needed the same reading
+    for /airlevelcheck/vs/0's lastSensingTime -- promoted here rather than
+    cross-imported, matching how filter_usage_percent was shared."""
+    try:
+        return datetime.fromtimestamp(float(value), tz=UTC)
+    except (TypeError, ValueError, OSError):
+        return None
+
+
 def filter_usage_percent(rep):
     """Filter usage as a percentage of rated capacity. Several families
     (AC, air purifier) report `filterUsage` as a raw count in
diff --git a/custom_components/localthings/registry/capabilities/range_hood.py b/custom_components/localthings/registry/capabilities/range_hood.py
index 6277859..fb2e215 100644
--- a/custom_components/localthings/registry/capabilities/range_hood.py
+++ b/custom_components/localthings/registry/capabilities/range_hood.py
@@ -7,8 +7,6 @@ brightness remain separate controls because the device advertises them as two
 independent fields.
 """
 
-from datetime import UTC, datetime
-
 from ..batch import is_stub_rep
 from ..capability import Capability
 from ..entities import (
@@ -19,14 +17,7 @@ from ..entities import (
     SensorDesc,
     SwitchDesc,
 )
-from .common import int_or_none, sensor_item_value
-
-
-def _timestamp(value):
-    try:
-        return datetime.fromtimestamp(float(value), tz=UTC)
-    except (TypeError, ValueError, OSError):
-        return None
+from .common import epoch_to_utc, int_or_none, sensor_item_value
 
 
 def _active_alarm_codes(items):
@@ -286,7 +277,7 @@ AIR_LEVEL_CHECK = Capability(
             field="x.com.samsung.da.lastSensingTime",
             device_class="timestamp",
             entity_category="diagnostic",
-            value_fn=_timestamp,
+            value_fn=epoch_to_utc,
         ),
         SensorDesc(
             key="last_air_sensing_level",
diff --git a/custom_components/localthings/translations/cs.json b/custom_components/localthings/translations/cs.json
index 0d7c11b..dc3fcbd 100644
--- a/custom_components/localthings/translations/cs.json
+++ b/custom_components/localthings/translations/cs.json
@@ -191,6 +191,9 @@
       "oven_setpoint": {
         "name": "Požadovaná teplota"
       },
+      "sensing_interval": {
+        "name": "Interval AI Purify"
+      },
       "setpoint": {
         "name": "Požadovaná teplota"
       },
@@ -494,6 +497,14 @@
       "rinse_cycles": {
         "name": "Počet máchání"
       },
+      "sensing_mode": {
+        "name": "Akce AI Purify",
+        "state": {
+          "off": "Pouze měření",
+          "airpurify": "Automatické čištění",
+          "alarm": "Dostat upozornění"
+        }
+      },
       "softener_concentration": {
         "name": "Koncentrace aviváže",
         "state": {
@@ -1030,6 +1041,12 @@
       "display": {
         "name": "Displej"
       },
+      "periodic_air_sensing": {
+        "name": "AI Purify"
+      },
+      "periodic_sensing_skip_status": {
+        "name": "Přeskočení měření AI Purify"
+      },
       "pet_filter_activation": {
         "name": "Aktivace filtru pro domácí mazlíčky"
       },
@@ -1199,6 +1216,12 @@
       },
       "night_start": {
         "name": "Začátek nočního osvětlení"
+      },
+      "sensing_skip_end": {
+        "name": "Konec přeskočení měření AI Purify"
+      },
+      "sensing_skip_start": {
+        "name": "Začátek přeskočení měření AI Purify"
       }
     },
     "water_heater": {
diff --git a/custom_components/localthings/translations/en.json b/custom_components/localthings/translations/en.json
index efea0a9..591019d 100644
--- a/custom_components/localthings/translations/en.json
+++ b/custom_components/localthings/translations/en.json
@@ -191,6 +191,9 @@
       "oven_setpoint": {
         "name": "Setpoint"
       },
+      "sensing_interval": {
+        "name": "AI Purify interval"
+      },
       "setpoint": {
         "name": "Setpoint"
       },
@@ -494,6 +497,14 @@
       "rinse_cycles": {
         "name": "Rinse cycles"
       },
+      "sensing_mode": {
+        "name": "AI Purify action",
+        "state": {
+          "off": "Sensing only",
+          "airpurify": "Auto clean",
+          "alarm": "Get notified"
+        }
+      },
       "softener_concentration": {
         "name": "Softener concentration",
         "state": {
@@ -1030,6 +1041,12 @@
       "display": {
         "name": "Display"
       },
+      "periodic_air_sensing": {
+        "name": "AI Purify"
+      },
+      "periodic_sensing_skip_status": {
+        "name": "AI Purify sensing skip"
+      },
       "pet_filter_activation": {
         "name": "Pet filter activation"
       },
@@ -1199,6 +1216,12 @@
       },
       "night_start": {
         "name": "Night light start"
+      },
+      "sensing_skip_end": {
+        "name": "AI Purify sensing skip end"
+      },
+      "sensing_skip_start": {
+        "name": "AI Purify sensing skip start"
       }
     },
     "water_heater": {
diff --git a/custom_components/localthings/translations/es.json b/custom_components/localthings/translations/es.json
index c45af0b..b7728e3 100644
--- a/custom_components/localthings/translations/es.json
+++ b/custom_components/localthings/translations/es.json
@@ -313,6 +313,9 @@
       "oven_setpoint": {
         "name": "Punto de ajuste"
       },
+      "sensing_interval": {
+        "name": "Intervalo de AI Purify"
+      },
       "setpoint": {
         "name": "Punto de ajuste"
       },
@@ -616,6 +619,14 @@
       "rinse_cycles": {
         "name": "Aclarados"
       },
+      "sensing_mode": {
+        "name": "Acción de AI Purify",
+        "state": {
+          "off": "Solo medición",
+          "airpurify": "Limpieza automática",
+          "alarm": "Recibir notificación"
+        }
+      },
       "softener_concentration": {
         "name": "Concentración del suavizante",
         "state": {
@@ -1152,6 +1163,12 @@
       "display": {
         "name": "Pantalla"
       },
+      "periodic_air_sensing": {
+        "name": "AI Purify"
+      },
+      "periodic_sensing_skip_status": {
+        "name": "Omisión de medición de AI Purify"
+      },
       "pet_filter_activation": {
         "name": "Activación de filtro para mascotas"
       },
@@ -1321,6 +1338,12 @@
       },
       "night_start": {
         "name": "Inicio de la luz nocturna"
+      },
+      "sensing_skip_end": {
+        "name": "Fin de la omisión de medición de AI Purify"
+      },
+      "sensing_skip_start": {
+        "name": "Inicio de la omisión de medición de AI Purify"
       }
     },
     "water_heater": {
diff --git a/custom_components/localthings/translations/it.json b/custom_components/localthings/translations/it.json
index d8939cb..e904333 100644
--- a/custom_components/localthings/translations/it.json
+++ b/custom_components/localthings/translations/it.json
@@ -191,6 +191,9 @@
       "oven_setpoint": {
         "name": "Valore impostato"
       },
+      "sensing_interval": {
+        "name": "Intervallo AI Purify"
+      },
       "setpoint": {
         "name": "Valore impostato"
       },
@@ -494,6 +497,14 @@
       "rinse_cycles": {
         "name": "Risciacquo"
       },
+      "sensing_mode": {
+        "name": "Azione AI Purify",
+        "state": {
+          "off": "Solo rilevamento",
+          "airpurify": "Pulizia automatica",
+          "alarm": "Ricevi notifica"
+        }
+      },
       "softener_concentration": {
         "name": "Concentrazione ammorbidente",
         "state": {
@@ -1030,6 +1041,12 @@
       "display": {
         "name": "Display"
       },
+      "periodic_air_sensing": {
+        "name": "AI Purify"
+      },
+      "periodic_sensing_skip_status": {
+        "name": "Esclusione rilevamento AI Purify"
+      },
       "pet_filter_activation": {
         "name": "Attivazione filtro animali"
       },
@@ -1199,6 +1216,12 @@
       },
       "night_start": {
         "name": "Inizio luce notturna"
+      },
+      "sensing_skip_end": {
+        "name": "Fine esclusione rilevamento AI Purify"
+      },
+      "sensing_skip_start": {
+        "name": "Inizio esclusione rilevamento AI Purify"
       }
     },
     "water_heater": {
diff --git a/custom_components/localthings/translations/nl.json b/custom_components/localthings/translations/nl.json
index 63614a1..45e1a68 100644
--- a/custom_components/localthings/translations/nl.json
+++ b/custom_components/localthings/translations/nl.json
@@ -191,6 +191,9 @@
       "oven_setpoint": {
         "name": "Instelpunt"
       },
+      "sensing_interval": {
+        "name": "AI Purify-interval"
+      },
       "setpoint": {
         "name": "Instelpunt"
       },
@@ -494,6 +497,14 @@
       "rinse_cycles": {
         "name": "Spoelcycli"
       },
+      "sensing_mode": {
+        "name": "AI Purify-actie",
+        "state": {
+          "off": "Alleen meten",
+          "airpurify": "Automatisch reinigen",
+          "alarm": "Melding ontvangen"
+        }
+      },
       "softener_concentration": {
         "name": "Concentratie wasverzachter",
         "state": {
@@ -1030,6 +1041,12 @@
       "display": {
         "name": "Display"
       },
+      "periodic_air_sensing": {
+        "name": "AI Purify"
+      },
+      "periodic_sensing_skip_status": {
+        "name": "AI Purify meting overslaan"
+      },
       "pet_filter_activation": {
         "name": "Huisdierfilter actief"
       },
@@ -1199,6 +1216,12 @@
       },
       "night_start": {
         "name": "Start nachtverlichting"
+      },
+      "sensing_skip_end": {
+        "name": "Einde AI Purify meting overslaan"
+      },
+      "sensing_skip_start": {
+        "name": "Start AI Purify meting overslaan"
       }
     },
     "water_heater": {
diff --git a/tests/fixtures/golden/air_purifier_avt_ww.json b/tests/fixtures/golden/air_purifier_avt_ww.json
index 8f13b0e..cc98a76 100644
--- a/tests/fixtures/golden/air_purifier_avt_ww.json
+++ b/tests/fixtures/golden/air_purifier_avt_ww.json
@@ -1,5 +1,6 @@
 {
   "state_keys": [
+    "air_sensing_state",
     "alarm_code",
     "clean_level",
     "device_active",
@@ -10,9 +11,17 @@
     "firmware_update",
     "hepa_filter_status",
     "hepa_filter_usage",
+    "last_air_sensing_level",
+    "last_air_sensing_time",
     "mute_once",
     "odor",
+    "periodic_air_sensing",
+    "periodic_sensing_skip_status",
     "power_switch",
+    "sensing_interval",
+    "sensing_mode",
+    "sensing_skip_end",
+    "sensing_skip_start",
     "super_fine_dust",
     "wind_strength_fan"
   ]
diff --git a/tests/fixtures/golden/air_purifier_tp1x_da_ac_air.json b/tests/fixtures/golden/air_purifier_tp1x_da_ac_air.json
index b72b83a..5337d36 100644
--- a/tests/fixtures/golden/air_purifier_tp1x_da_ac_air.json
+++ b/tests/fixtures/golden/air_purifier_tp1x_da_ac_air.json
@@ -1,5 +1,6 @@
 {
   "state_keys": [
+    "air_sensing_state",
     "alarm_code",
     "child_lock",
     "clean_level",
@@ -14,11 +15,18 @@
     "firmware_update",
     "hepa_filter_status",
     "hepa_filter_usage",
+    "last_air_sensing_level",
+    "last_air_sensing_time",
     "mute_once",
     "odor",
     "panel_status",
+    "periodic_air_sensing",
+    "periodic_sensing_skip_status",
     "pet_filter_activation",
     "power_switch",
+    "sensing_mode",
+    "sensing_skip_end",
+    "sensing_skip_start",
     "sound_mode",
     "sound_output",
     "sound_volume",
diff --git a/tests/fixtures/golden/air_purifier_vtww.json b/tests/fixtures/golden/air_purifier_vtww.json
index 9970ed3..d2949b8 100644
--- a/tests/fixtures/golden/air_purifier_vtww.json
+++ b/tests/fixtures/golden/air_purifier_vtww.json
@@ -1,5 +1,6 @@
 {
   "state_keys": [
+    "air_sensing_state",
     "alarm_code",
     "clean_level",
     "device_active",
@@ -9,8 +10,16 @@
     "firmware_update",
     "hepa_filter_status",
     "hepa_filter_usage",
+    "last_air_sensing_level",
+    "last_air_sensing_time",
     "odor",
+    "periodic_air_sensing",
+    "periodic_sensing_skip_status",
     "power_switch",
+    "sensing_interval",
+    "sensing_mode",
+    "sensing_skip_end",
+    "sensing_skip_start",
     "super_fine_dust",
     "wind_strength_fan"
   ]
diff --git a/tests/test_air_purifier_airlevelcheck.py b/tests/test_air_purifier_airlevelcheck.py
new file mode 100644
index 0000000..8410025
--- /dev/null
+++ b/tests/test_air_purifier_airlevelcheck.py
@@ -0,0 +1,263 @@
+"""Tests for /airlevelcheck/vs/0 -- the "AI Purify" periodic air-quality
+sensing engine (issues #84 and #190).
+
+The resource is reported by three of this registry's four board families, so
+the read assertions run against each family's own fixture; the write contracts
+were exercised on AVT-WW-TP1-23-AXX500 hardware and are asserted here through
+the descriptors that carry them.
+"""
+
+import datetime
+
+from custom_components.localthings.registry.adapter import flatten
+from custom_components.localthings.registry.by_type import resolve
+from custom_components.localthings.registry.capabilities import air_purifier
+from custom_components.localthings.registry.discovery import discover
+from tests.conftest import _load_device
+
+# The three fixtures whose dumps carry this resource. air_purifier (the
+# ARTIK051_TVTL family, issue #56) has no such href and is deliberately absent.
+FAMILIES = ("air_purifier_avt_ww", "air_purifier_vtww", "air_purifier_tp1x_da_ac_air")
+
+HREF = ["airlevelcheck", "vs", "0"]
+
+
+def _rep(fixture):
+    return _load_device(fixture)["/airlevelcheck/vs/0"]
+
+
+def _state(fixture):
+    resources = _load_device(fixture)
+    reg = resolve(resources)
+    assert reg is not None and reg.name == "air_purifier", fixture
+    return flatten(discover(resources, reg.capabilities, reg.pattern_capabilities), resources)
+
+
+def _desc(key):
+    return next(d for d in air_purifier.AIR_LEVEL_CHECK.entities if d.key == key)
+
+
+def test_air_level_check_is_bound_not_covered():
+    """The href used to sit in COVERAGE as opaque scheduler plumbing. Guard
+    against it being covered again, which would silently drop every entity
+    below while still reporting zero unbound hrefs."""
+    covered = {cap.href for cap in air_purifier.COVERAGE}
+    assert "/airlevelcheck/vs/0" not in covered
+
+
+def test_every_reporting_family_binds_the_cluster():
+    for fixture in FAMILIES:
+        state = _state(fixture)
+        for key in (
+            "sensing_mode",
+            "periodic_air_sensing",
+            "periodic_sensing_skip_status",
+            "sensing_skip_start",
+            "sensing_skip_end",
+            "air_sensing_state",
+            "last_air_sensing_time",
+            "last_air_sensing_level",
+        ):
+            assert key in state, f"{fixture}: {key}"
+
+
+def test_tvtl_family_is_untouched():
+    """Issue #56's board has no /airlevelcheck href at all -- nothing this
+    change adds may appear on it."""
+    state = _state("air_purifier")
+    for key in ("sensing_mode", "periodic_air_sensing", "sensing_interval", "sensing_skip_start"):
+        assert key not in state, key
+
+
+def test_no_unbound_hrefs_on_any_reporting_family():
+    for fixture in FAMILIES:
+        resources = _load_device(fixture)
+        reg = resolve(resources)
+        assert reg is not None, fixture
+        unbound = []
+        discover(resources, reg.capabilities, reg.pattern_capabilities, log=unbound.append)
+        assert unbound == [], f"{fixture}: {unbound}"
+
+
+# --- the two knobs are separate entities, not one folded control -------------
+
+
+def test_activation_and_action_are_separate_entities():
+    """The resource carries an on/off and an action as independent fields, and
+    the appliance's own UI presents them that way. Folding them into one
+    control would make a configured action invisible while the feature is off,
+    and would leave no way to toggle the feature without overwriting it."""
+    assert _desc("periodic_air_sensing").field == (
+        "x.com.samsung.da.periodicSensingActivationState"
+    )
+    assert _desc("sensing_mode").field == "x.com.samsung.da.autoExeState"
+
+
+def test_action_options_come_from_the_device_not_a_table():
+    """supportedAutoExeState is advertised on every reporting fixture, so the
+    select reads it rather than carrying a typed-in tuple -- a board adding a
+    fourth action is then accepted rather than rejected."""
+    desc = _desc("sensing_mode")
+    assert desc.options_field == "x.com.samsung.da.supportedAutoExeState"
+    assert not desc.options, "options must come from the device, not a static tuple"
+    for fixture in FAMILIES:
+        assert _rep(fixture)["x.com.samsung.da.supportedAutoExeState"] == [
+            "Off",
+            "Airpurify",
+            "Alarm",
+        ], fixture
+
+
+def test_action_write_sends_the_raw_advertised_value():
+    """select.py maps the chosen option back to the device's own casing before
+    calling write_fn, so the body is the advertised token verbatim."""
+    for raw in ("Off", "Airpurify", "Alarm"):
+        href, body = _desc("sensing_mode").write_fn(raw, {})
+        assert href == HREF
+        assert body == {"x.com.samsung.da.autoExeState": raw}
+
+
+def test_activation_write_leaves_the_action_alone():
+    """Toggling the feature must not disturb autoExeState -- that's what makes
+    the switch able to do something the action select can't."""
+    for payload, expected in (("On", "On"), ("Off", "Off")):
+        href, body = _desc("periodic_air_sensing").write_fn(payload, {})
+        assert href == HREF
+        assert body == {"x.com.samsung.da.periodicSensingActivationState": expected}
+        assert "x.com.samsung.da.autoExeState" not in body
+
+
+# --- interval ----------------------------------------------------------------
+
+
+def test_sensing_interval_only_where_the_field_exists():
+    """TP1X_DA-AC-AIR (issue #130) omits periodicSensingInterval; the other two
+    report it. The entity must follow the field, not the href."""
+    assert "sensing_interval" in _state("air_purifier_avt_ww")
+    assert "sensing_interval" in _state("air_purifier_vtww")
+    assert "sensing_interval" not in _state("air_purifier_tp1x_da_ac_air")
+
+
+def test_interval_is_minutes_in_the_ui_and_seconds_on_the_wire():
+    desc = _desc("sensing_interval")
+    assert desc.value_fn("600") == 10
+    assert desc.write_fn(10, {})[1] == {"x.com.samsung.da.periodicSensingInterval": "600"}
+
+
+def test_interval_keeps_zero_distinct_from_unknown():
+    """`if secs` would fold a reported 0 into None. Anything else nonzero
+    rounds up, so a sub-minute reading can't render as 0 and fall below the
+    entity's own floor."""
+    desc = _desc("sensing_interval")
+    assert desc.value_fn("0") == 0
+    assert desc.value_fn("20") == 1
+    assert desc.value_fn("61") == 2
+    assert desc.value_fn(None) is None
+
+
+def test_interval_floor_is_one_minute():
+    """lastSensingTime lands on an exact minute on this board family, so a
+    sub-minute interval is unobservable; and 0 has no established meaning
+    here, unlike the zero floors on oven.cook_time / delay_start_hours."""
+    desc = _desc("sensing_interval")
+    assert desc.native_min == 1
+    assert desc.write_fn(0, {}) is None
+    assert desc.write_fn(0.4, {}) is None
+    assert desc.write_fn(1, {})[1] == {"x.com.samsung.da.periodicSensingInterval": "60"}
+
+
+# --- skip window -------------------------------------------------------------
+
+
+def test_skip_time_splits_the_hhmmhhmm_window():
+    read_start = _desc("sensing_skip_start").value_fn
+    read_end = _desc("sensing_skip_end").value_fn
+    # Issue #190's unit ships a real window: 03:00-23:00.
+    assert read_start("03002300") == datetime.time(3, 0)
+    assert read_end("03002300") == datetime.time(23, 0)
+    # Issue #84's unit sits at the inert default.
+    assert read_start("00000000") == datetime.time(0, 0)
+    # Junk and short strings read as unknown rather than raising.
+    assert read_start("") is None
+    assert read_start("99999999") is None
+    assert read_end("0300") is None
+
+
+def test_skip_time_write_preserves_the_other_half():
+    rep = {"x.com.samsung.da.periodicSensingSkipTime": "03002300"}
+    _, body = _desc("sensing_skip_start").write_fn(datetime.time(7, 30), rep)
+    assert body == {"x.com.samsung.da.periodicSensingSkipTime": "07302300"}
+    _, body = _desc("sensing_skip_end").write_fn(datetime.time(22, 5), rep)
+    assert body == {"x.com.samsung.da.periodicSensingSkipTime": "03002205"}
+    # A board that has never had a window set still round-trips.
+    _, body = _desc("sensing_skip_end").write_fn(datetime.time(1, 2), {})
+    assert body == {"x.com.samsung.da.periodicSensingSkipTime": "00000102"}
+
+
+def test_skip_time_write_normalizes_a_half_it_cannot_parse():
+    """Padding alone would splice a malformed half straight back onto the wire.
+    The read side already refuses one, so the write side zeroes it instead of
+    echoing junk to the device."""
+    junk = {"x.com.samsung.da.periodicSensingSkipTime": "0730zzzz"}
+    _, body = _desc("sensing_skip_start").write_fn(datetime.time(8, 0), junk)
+    assert body == {"x.com.samsung.da.periodicSensingSkipTime": "08000000"}
+    junk = {"x.com.samsung.da.periodicSensingSkipTime": "zzzz2200"}
+    _, body = _desc("sensing_skip_end").write_fn(datetime.time(23, 0), junk)
+    assert body == {"x.com.samsung.da.periodicSensingSkipTime": "00002300"}
+
+
+def test_skip_status_switch_body():
+    assert _desc("periodic_sensing_skip_status").write_fn("On", {})[1] == {
+        "x.com.samsung.da.periodicSensingSkipStatus": "On"
+    }
+
+
+# --- read-only diagnostics ---------------------------------------------------
+
+
+def test_last_sensing_time_reads_as_utc():
+    state = _state("air_purifier_avt_ww")
+    assert state["last_air_sensing_time"].tzinfo is not None
+    assert state["last_air_sensing_time"].year >= 2020
+
+
+def test_read_only_keys_match_the_range_hood_capability():
+    """The three read-only sensor keys are shared with the hood deliberately,
+    so both families read from one translation catalog entry each. If either
+    side renames one, this catches the drift.
+
+    periodic_air_sensing is excluded: it's a SwitchDesc here and a
+    BinarySensorDesc on the hood, so the two sit in different platform
+    catalogs and are worded differently -- see the next test.
+    """
+    from custom_components.localthings.registry.capabilities import range_hood
+
+    hood = {d.key for d in range_hood.AIR_LEVEL_CHECK.entities}
+    ours = {d.key for d in air_purifier.AIR_LEVEL_CHECK.entities}
+    assert {
+        "air_sensing_state",
+        "last_air_sensing_time",
+        "last_air_sensing_level",
+    } <= hood & ours
+
+
+def test_periodic_air_sensing_is_writable_here_and_read_only_on_hoods():
+    """The reason range_hood.AIR_LEVEL_CHECK is not imported directly: the hood
+    models this key as a read-only BinarySensorDesc, this board needs a
+    writable SwitchDesc. Reusing the hood's capability would migrate every hood
+    user's entity to a different platform."""
+    from custom_components.localthings.registry.capabilities import range_hood
+    from custom_components.localthings.registry.entities import BinarySensorDesc, SwitchDesc
+
+    hood = next(d for d in range_hood.AIR_LEVEL_CHECK.entities if d.key == "periodic_air_sensing")
+    assert isinstance(hood, BinarySensorDesc)
+    ours = _desc("periodic_air_sensing")
+    assert isinstance(ours, SwitchDesc)
+    assert ours.write_fn is not None
+
+
+def test_read_only_diagnostics_match_the_hood_on_visibility():
+    """The hood leaves all three enabled; asserting key parity with it while
+    hiding two of them would be a quiet divergence."""
+    for key in ("air_sensing_state", "last_air_sensing_time", "last_air_sensing_level"):
+        assert _desc(key).enabled_default is True, key