Freeze Detection

Freeze Detection

A frozen device is the failure no other integration or blueprint can catch: in Home Assistant, a freeze occurs when a device stops reporting and every entity continues to show the last value the device recorded. What it looks like is a temperature sensor reading 21 degrees, or a door sensor reporting closed, forever. Everything looks fine, and nothing is.

Device Sentinel catches this, along with the plainer cases where a device becomes unavailable or unknown.

The Four Ways a Device Can Be Down

Device Sentinel categorizes a down device into one of four states based on what its entities show and how long it has been silent:

• Frozen: The device has stopped reporting, but its entities still show their last values.
• Unavailable: Every live entity on the device reads unavailable.
• Unknown: Every live entity on the device reads unknown.
• Not reported: Since the device was first discovered by the integration, it has never shown any activity at all. This is an important category because the integration can learn no rhythm from a device with no activity.

The liveness rule: Underneath all of these is a single rule: if any live entity on a device reports a real value, the device is alive, no matter how many of its sibling entities have dropped. A device is only considered down when nothing on it is reporting. If a down device shows a mix, some entities unavailable and some frozen, it takes its worst category, because a device with most of its entities unavailable is a dead device whose others simply have not caught up yet.

How a Device Is Judged

Every device is measured against its own learned rhythm, never a fixed or chosen timeout.

Device Sentinel will learn a device's reporting rhythm as soon as it is installed. A device that reports every 30 seconds is judged on a scale of minutes; a device that reports twice a day is judged on a scale of hours. No single timeout could be right for both.

The freeze window: The window is the device's learned rhythm plus a grace margin. A device is flagged frozen when it is silent past this window while its entities still hold stale values.

Arming: A device is only judged frozen once it has learned enough days to have a trustworthy rhythm. Until then, it is watched for unavailable and unknown states only, because a device with no established rhythm has no window to miss. Devices with no natural heartbeat, like buttons that only speak when pressed, learn a very long rhythm and so are effectively never called frozen for ordinary quiet.

Tuning the Window: The Grace Sliders

The grace margin added to the learned rhythm follows a curve you shape with two sliders on the Freeze Detection configuration screen. The rhythm itself is measured, never chosen; these sliders only tune how patient the integration should be past each device's own normal.

• Delta Low (1 to 8 minutes, default 3): The grace a fast device gets. This keeps a chatty device from being called dead just for missing a couple of routine reports. Raise this if a chatty device is being flagged too soon.
• Delta High (4 to 12 hours, default 8): The grace a slow device gets. This catches the slowest devices in a bounded time. Lower this if a slow device should be caught faster.

These sliders do not just cap the ends; they shape the whole curve between them, so moving either re-tunes every device in the fleet. At the defaults, a device that reports roughly once an hour gets about double its normal rhythm before it is flagged.

The Most Accurate Clock: Last-Seen Entities

For the most reliable freeze clock, press Enable Last Seen on the device page.

Where a device has a last-seen entity, that entity is the clock. It is the coordinator's own record of when it last heard from the device, meaning a bridge or hub republishing a last known state cannot make a silent device look alive. Most integrations ship last-seen entities disabled by default. Turning them on, which the buttons do for you, is the single most useful action you can take for freeze accuracy.

Surviving restarts: A freeze in progress survives a restart because the silence is measured from Device Sentinel's own clock, not a value Home Assistant resets at every reboot. Detection is live: a device flagged at 11 AM shows at 11 AM, and the moment it genuinely reports again, the flag clears.

What Happens When a Device Goes Down

When a device is detected frozen, unavailable, or unknown, it is added to the problem list as a new item, the device-family phone push fires, and both of the integration's storage files are saved. Each silence past its window is recorded as a row in the silence_episodes diagnostics report, noting its duration, what ended it, and what it taught the statistics. A mysterious recovery while flagged is capped, so it cannot widen a device's freeze window unchecked; see The Diagnostic Reports for more information.

• The daily brief's Now section shows what is in trouble at the moment it is written, worst first, or an all-clear line.
• The count entity: The Device: Frozen count reports how many devices are down right now, with each one's category and duration carried in its attributes. It ships disabled by default because the problem list is the intended place to read this data, but you can enable it from the entities page if you want it on a dashboard.

Freeze Muting

This configuration screen carries a freeze mute list using the same three tiers as the others: by integration, by label, or by single device.

A freeze-muted device keeps its clock and its learned rhythm, because it is still watched and re-including it is instant. It is simply never given a freeze, unavailable, unknown, or not-reported verdict in any report or notification.

In the telemetry report, a muted device's STATUS reads "Muted (FRZ)".

How it interacts: When you mute at a broader level, like an integration, everything it covers disappears from the narrower lists.

Versus Exclusions and Muting: A globally muted device is judged by nothing at all and does not even appear in the freeze lists. Use freeze muting when you want a device watched for battery and signal but not called down; use Exclusions and Muting when you want it left alone entirely.