The BBT-2500 dual beam sensor from Dakota Alert features a solar powered dual beam detector with built in rechargeable batteries. When both beams are broken a wireless alarm signal is sent up to 2500 feet to the chime receiver. The BBT-2500 system operates on the same frequency as all Dakota Alert 2500 products. This means you can expand your existing Dakota Alert system with the new photo beam sensors. Never worry about changing batteries again! These BBT-2500 wireless beam sensors come complete with a solar panel and built in rechargeable batteries ensuring the system is always operational.