I have been using and recommending the “CPR Metronome” Android phone app (also available for I-Phone) for a couple of years. The app is easy to use and can be set to open and start on tap. It can also run in the background while using the phone to talk to 9-1-1 EMS Dispatch for help and guidance.
CPR Metronome will prompt you with the correct rhythm and rate for optimal compressions and breaths. Really – how long can you hum “Staying Alive . . .” ? Of course, proper training can prepare you for the realities of CPR and this app may help you perform this possibly life-saving skill.
https://play.google.com/store/apps/developer?id=narumikuro
M•Stephenson: Licensed Paramedic, Wilderness EMT, Chief Fire Officer, Instructor