Simple Metronome, it has a clip so you can clip it to your belt/pants.
I use it with a headphone to practice with the band.
I has a headphone output, but the overall volume is not so loud, so if your band is very loud (even with headphones) , you will have trouble hearing the metronome !
Smaller version of the RW-200, no fancy settings possible, just on and of (as it is supposed to do!)