samer wroteI would like to build this or find an alternative solution. I think it would make a nice gift to a friend whose birthday is coming up.
@mesa: you seem to have overlooked an important requirement. The vibrating motor needs to be activated at a certain hour.
All you need is a digital timer and you're good to go.
But J4D has a point, we have to consider the bulkness of the electronics. The wrist band is easy to manufacture from velcro, but where to place the electronics? There is the idea of conductive fabric which can be used to double as a breadboard and a clothing encasing for the electronics and vibrating motor:
I'll think it over...