Beats are detected with a microphone and converted to other actions with this device.. It can switch with a reed relay, send out serial (like midi or such) and it sends out key presses with the keypad.
I mainly use it for visual stuff that i do. Like the Browser Jockey Project, or any of my Visual-Equipments. One of the things i spend some time on to get it to work o.k. was the automatic volume adjustment, so if the music volume changes the threshold will adapt.