On the hardware front, Growl is divided into two main parts. There’s a frame that’s designed to be screwed to your wall. You then attach a boxing bag component onto the frame. Most of the sensing intelligence is located in the frame. The boxing bag itself is mostly made of foam and artificial leather, with five or six accelerometers inside to detect punching power etc.
The frame includes a key component of the device: a 4K projector. It can project a human-sized coach onto the boxing bag and various metrics on the wall. Growl has also been using the projector for a gaming experience (think Tap Tap Revenge on a boxing bag).