I bought an old blocked S4 mini about 3 years ago for £10, installed Alfred camera on it and on my iPhone and Shield TV and set it up in position keeping it plugged in to power while turning off the screen.
It’s been super useful for monitoring garden/pets and stuff, I could imagine better models being better resolution, but it’s definitely a useful way to recycle old useless phones, as you can hook up as many as you want.