Heh, if your like me and you dont want to hastle with odd batteries or "mercury switches", you can simply put two exposed metal pads at the base of the RF, on on the RF and the other at the bottom where it rests on the ear, when it is down, they touch and the circut is completed (that means it flashes) and by this method you can use AAs or some such more common battery that also wont be added weight in the RF.