This simple and practical milestone adjustable arm band light is a safety light for night time running walking or even cycling simply tighten it around your arm and decide if you want it to flash or be on permanently and away you go the replaceable cr2032 batteries will operate for 72hrs on continuous mode or 96hrs flashing so should last for a few trips out and about when in poorly lit areas no complicated mechanisms just slip onto your arm and adjust the strap to ensure it stays in place