Buyer beware: You can only use the Tria if you have light- or medium-toned skin and dark hair. (Dark complexions absorb too much laser energy, which can cause skin damage, and light hair doesn't have enough pigment to absorb the follicle-killing light.) The laser comes with a small skin sensor—if you get a green light when you press it against your skin, you're in business. Also, if you want to remove hair on a large area, you'll need to have a whole lot of time on your hands. The Tria's laser beam is only about one centimeter squared, so it's most practical on the armpits or bikini line (it's not approved for use on the face).