As I rode my bike in to work yesterday I realized earphones are not a great idea if you want to know when someone is coming up on you from behind. When I ride my bike I slow down, ring my bell and say 'on your left'. But that still is not enough when someone is listening to music turned up and both ears having ear buds. Sorry to those I startle as I pass but, I did try to warn you. I recommend to at least keep one ear open - the left ear on the passing side so you can hear when a cyclist or runner is approaching from behind.