The Tempo Batteryless Acoustic Amplifier is simply a Battery Free Acoustic Amplifier for iPhone4 and 4S. It slips onto the bottom of the phone and channels the sound from the internal speakers in such a way that it increases the volume. I estimate that the increase is about 3-4 db, which is noticeable. There is also an audible improvement in the clarity of the music once the Tempo is attached. No electronics or batteries are involved.