Add "last_seen" entity for all Zigbee devices

[emogenet]

This is a feature request.

It would be very nice if every zigbee request would expose its "last_seen" internal property as a proper HA entity.

Maybe disabled by default, like LQI and RSSI are, but still around in case the user wants to use it.

Currently, it is not possible to get notified when a device "pings".

And therefore, it is hard to build efficient automations that, for example, discover unresponsive / disconnected zigbee devices or monitor and automatically gather status on how often a sensor emits data

Also, either when building a new network of zigbee devices, or operating an existing one, it would be super useful to be able to automatically discover orphaned or ill-connected devices and notify the user (very useful for e.g. battery-operated devices or devices that are flaky because their connection is obstructed).

[puddly]

I think we can do that. There are a few potential issues, however. last_seen as an entity wouldn't necessarily correspond to attribute updates for a lot of devices for a few reasons:

• it's updated when a device sends anything, even poll control cluster check-ins or OTA cluster image requests.
• device update frequency isn't static, devices are configured to update at least once every X minutes, no more than once every Y minutes, every time an attribute changes by Z. These values depend on the specific attribute but in effect, the device will report an unchanging value every X minutes no matter what but still update you more rapidly when things really change.

It's a little difficult to predict exactly how battery powered devices go offline but there are a few ways we can do so for modern devices that are much more accurate than the current logic of "offline if not heard from for four hours".

[emogenet]

So, to be clear: for me what matters if we turn last_seen into some sort of "synthetic" attribute that corresponds to an HA entity, it is not that it corresponds to any actual attribute update.

What matters is to be notified when the device "pings", that is it somehow tells the zigbee network that it is alive so we can monitor for failing devices or devices with flaky connections (by aggregating statistics on the "last_seen" entity).

it's updated when a device sends anything,

That's exactly what I want to be notified about.

device update frequency isn't static

yes, indeed, all the more reason to be able to catch these as asynchronous events

It's a little difficult to predict exactly how battery powered devices go offline

Not sure why you'd want to try and predict that. Quite the contrary: as it is rather unpredictable, if last_seen becomes an entity you can listen to, then you can log these updates and learn exactly how the device behaves over time by looking at the history of the "last_seen" entity.

Just to make sure I made myself clear in my original message, and apologies if I'm laying it on a bit thick: my feature request is that when the ZHA code receives a message, any kind of message from the device, it should create an event for the synthetic entity "last_seen".

[TheJulianJES]

Since Z-Wave has a (disabled by default) "last seen" timestamp entity, I agree that it makes sense for us to also have one.

I've only recently started playing with Z-Wave, but I believe it does not mark all entities as unavailable if the node is "dead" since home-assistant/core#148611. What's mentioned in that PR doesn't really apply to us, as battery-powered Zigbee devices still report in often enough for us. The timeouts until ZHA marks device entities as unavailable are also configureable and already really long for end-devices by default.

For a possible implementation, we'd also need to make sure the "last seen" timestamp entity is not made unavailable when ZHA thinks the device is unavailable. Otherwise, that entity would be relatively useless.

Lastly, when ZHA considers a device as unavailable, you'll get a zha_event with an device_event_type of device_offline. You can already create automations to get alerted when devices become unavailable. There's also a blueprint available here: https://gist.github.com/dmulcahey/6a231d57ba1335fe4cd12b35366fae84

[emogenet]

Hi everyone,

I did a bit of digging and found this PR:

home-assistant/core#14579

In it, it looks like what I'm after was already implemented, but at the end, last_seen as an entity was removed because it would be updated too often.

My suggestion: why not revive this work and instead choose to disable "last_seen" by default like we do for RSSI and LQI ? Wouldn't it be strictly better or is there a downside I am not seeing?