It’s a project called snapVCC, and it turns a 9 volt battery into a regulated 3.3 or 5 volt supply. The idea behind snapVCC is simple enough; just add a circuit board to the top of a nine volt ...

The whole circuit, complete with tiny speaker and an LED to indicate pulses, sits neatly on top of a 9-volt battery. The video below shows it in action with a test source.