Hi,
Which things can I do with an old android phone ? Like a Xiaomi mi a3.
Take the battery out of it. Put on lineage OS. Use it as a microserver, mine some crypto like monero. Because it’s CPU-based. You could use it as a remote for other devices. You could use it as a webcam for your house. It can do everything it used to do.
Old lithium batteries become a fire hazard, so I would recommend removing it if you can. Or at least replacing it with the new battery. Good practice at least even if you break it
Leaving an airplane mode, don’t use the cellular modem, you’re not getting any hardware driver updates. So it’s security risk. Don’t do anything too sensitive with it. But just for you around home network it’s fine
large hardware support portfolio, i think its the single most widely compatible ROM. As long as one crazy maintainer hangs on to your device, you will get lineage updates.
Just because you forgo hardware driver security updates, doesn’t mean you should stop getting android security updates.
Depends on the design of the phone. Some will work just fine off of USB power. Some will try to detect a battery and then fail the boot. For the ones that are more troublesome you’ll have to Google the instructions on to make a dummy battery load. The important thing is to get the lithium ion battery out of the circuit.
Make it a server/put LineageOS on it.
I do same. Don’t got any accounts logged in either on it and just runs f-droid apps and Aurora store. It’s reason I value physical Sims since it makes it easy to swap when I need to without having to sign in to anything, since it’s my accountless phone that if I lost has nothing of importance in it.
Backup
I use mine as a camera in the garage when I’m working on my car so I don’t get my current phone all greasy.