Many years ago,I had studied Dual H-bridge motor drive control by hacking cheap 4 channals toy remote control board and applied it to remote twin motors track and wheel set.Now I try to use Arduino controller with IR remote to control it again.That's also work.

This instructable show how to use an ATtiny85 to create a tiny watch core that can run over 1 year before recharge or replace battery.
The instruction to make the watch case may be in next instructable.
I have made a few Arduino watch before, but I found the watch using ATmega boards or ATmega chips are a little bit too big to wear. So I would like to make it with a smaller chips.

I hacked a simple audio recorder and playback system, rigged it to Arduino, and inserted it into a tin can phone that I installed by the door—now we can each leave a quick message to greet the other!
To record a message, press a pressure sensor on the outside of the can and speak into it. To listen, simply hold the can up to your ear. (It uses a light sensor to trigger playback!)
My ulterior motive was to learn how to hack existing electronics and control them with Arduino. It can be adjusted to use different sensors and be put in any sort of housing. I uploaded a quick demo for now; fuller video to come soon!