Is last_changed or last_update persistent across reboots?

Configuration
1

I am working on integrating HA into my monitoring system to detect entities who are not available and alert me.

In addition to tracking the unavailable state (which, if I understand correctly, is actively sought by HA for devices that set a state - such as wifi switches) I wanted to inquire about the last time HA saw a given device.

This is particularly important for sensors that just send values about themselves (no state).

I grabbed the states, for example

{
    "entity_id": "binary_sensor.waterleak_sdb_water_leak",
    "state": "off",
    "attributes": {
      "battery": 100,
      "battery_low": false,
      "last_seen": "2021-07-04T16:21:24.539Z",
      "linkquality": null,
      "tamper": false,
      "voltage": 3145,
      "water_leak": false,
      "friendly_name": "waterleak_sdb_water_leak",
      "device_class": "moisture"
    },
    "last_changed": "2021-08-13T20:50:27.709510+00:00",
    "last_updated": "2021-08-13T20:50:27.891332+00:00",
    "context": {
      "id": "c263882279523891c025d4e536c03fec",
      "parent_id": null,
      "user_id": null
    }
  },

I was suspicious about the dates provided by last_chnaged or last_updated because Zigbee2MQTT (the bridge between the sensor and MQTT) reports the device missing for a month (vs ~48h above).

I then had a look at another entity that is missing for ages, and it reports the same time!

My question: is the date persistent? If not - can I make it persistent?

I use HA in a docker container with a persistent volume holding the whole “root” directory and everything below (this is the directory configuration.yaml is, including storage) - so the files do persist.

2

I realized right after posting that there is a last_seen attribute. I will look closer at that one.

3

no

Not that I know of.

4

To help make this persistent, please vote on this feature request: Retain last state change data of a sensor after reboot