Bracelet that allow you to control with your fingers device/gear actions

Hi guys, a friend of mine and I are trying to create a bracelet with some sensors that allows people to control other devices with their finger movements.

I got different doubts:

Do you think it can be useful with smartphones, tablets and similar devies (like switching songs, controlling remotes etc.)?

In case it does, how would you realize? a whole bracelet or just a module that can be put under the watchband?

Color? material?
thank you very much guys hope you can help me to sort it out!