Jonathan Thomson writes:
I made a device that charges my cell phone and plays an audio alert when it detects the phone is vibrating. I think this is useful for people who forget to take their phone off vibrate while it’s charging or the hard-of-hearing. It’s much louder than my cell phone’s speaker so it makes it easier to hear someone is calling even if the ringer is on. If this sort of device was more common people could leave their phone on vibrate almost all the time without worrying about missing a call.
Vibe2Tone – using an ATtiny85 available - [Link]