Linda, My understanding of the technology involved here is that they are a passive device similar to the electronic security tags that you'll find on merchandise in the store. They are also like the pass keys used on some toll roads or the ones you wave in front of the gas pump at Mobil gas stations. No battery required. They just echo back to the sending device be it your car, gas pump, or security scanner at the store. Also have not heard of any problems with cell phone use and these devices.