Currently, the device tracker’s main usage is for tracking users around the house (and in other locations). However, the information provided by the device tracker component can be useful in an additional way - to let other platforms know when a device comes online.
Practical examples from my personal experience:
- Yeelight WiFi bulbs. When these bulbs are turned off by a physical switch, they go offline. After turning them back on, it takes a while for HASS to recognize their presence and allow control from the interface (much longer than it takes the bulb to connect to WiFi).
- LG Smart TV and sources automation. I use an automation that changes the source of the receiver in accordance with the source of the TV. However, upon turning the TV on, it can take up to a minute or two for HASS to recognize that the LG WebOS device is online. Again, much longer than it takes the TV to connect to the network.
What I’d like to see, is an extension to (or a fork of) the Device Tracker component, that allows other platforms to subscribe to events of devices going online and offline, thus accelerating the detection of their online/offline status by the platforms.