This tiny device packs quite a punch! There is nothing more discrete~use it in public, it looks just like an Ipod touch and is as easy to use. Press up to change the mode (it has 6), down to change the timer, left and right to increase and decrease the intensity (10 possible levels) and it even has a pause button in the middle! This machine has 2 channels with 2.5 plug jacks. It has a 4.5Voutput and is powered by an internal lithium battery charged with a standard USB cable or ac/dc power adapter.