Slightly larger than a quarter and only weighing 7 grams, Princeton Tec's little Pulsar II still manages to pack a serious punch. Stash 1 in the car and 1 on every keychain, backpack and gear loop you own, and you'll never be without emergency light again. It uses an Ultrabright LED to give you up to 12 hours of run time. It works by either just squeezing the sides or stays on with a flick of the switch. It even comes in different color LEDS so have some fun with it.