Ask HN: Niche Uses for Disused Phone

[hyperific]

I've read 20 different lists that have common suggestions for disused phones like use it as a dedicated e-reader, a security camera, a dedicated android gaming device, a photo frame, etc. These are fine ideas but what is a project you made or are aware of that's "off the beaten path"?

[v0idcode]

makes a great brain for a small robot - i use usb-otg and a hand-rolled c io library, but ive seen lots of easy access projects like allowing an android to link with lego mindstorms (technic robotics kit) via a daughterboard of sorts