Coat-Button

May be found on tindie . The device can be equipped with either standard single-colour LEDs or dual-colour ones. The demo firmware supports a couple of modes, which can be cycled through by shorting the two center-most pins and applying power. The settings are stored in EEPROM.

The cables + battery placement need improvement, but the way the button itself is attached (no sowing required) is pretty good already. I like it. Documentation