This is just an extra headphone and does not include the base transmitter. The Sennheiser HDR 120 RF wireless headphones are an inexpensive supplementary or expansion set, operating in the 863MHz or 926MHz variant frequency range, and designed for use with Sennheiser's RS 120 Hi-Fi or television wireless headphone monitoring system. These headphones feature extended low frequency reproduction, a supra-aural, open-back design, and NiMH rechargeable battery operation with a 20 - 25 hr. battery life.