hardware query - looking for 2/3 button input device (micro USB or bluetooth)

I am looking for an input device with a few buttons, preferably large-ish, that can connect to an android phone via either micro-USB or bluetooth, and that I can respond to button press events in an app.

The example usage is the user having the thing in an accessible pocket, and using it to control the app on the phone which is in another (possibly less accessible) pocket.
Think of, say, an actor discreetly pressing it that causes the app to speak the next line off a cue sheet.

I'm ok (or probably will be) with the software/API side of things, but I want to start with the hardware - I just don't know what device I can use.

A keyboard would do, but it is too big and has too many keys.