Specifications: Color: Black Transmission Type: Wireless Expandable with additional transmitters: yes Range in open area: 200m Other features: learning system Receiver Receiver power type: mains (230V) Number of ringtones: 36 Ringer Volume Level (dB): 60-90 - Volume control: yes Optical signaling: yes Receiver dimensions - width (mm): 81 mm Receiver dimensions - height (mm): 81 mm Receiver dimensions - depth (mm): 35 mm Transmitter: Transmitter Power Type: Battery-Free Battery included: no Transmitter Rating: IP44 Transmitter dimensions - width: 50 mm Transmitter dimensions - height: 82 mm Transmitter Dimensions - Depth: 21.5 mm The set of two wireless doorbells with battery-free button is designed to be used in homes, apartments, offices, hospitals, shops, etc. No doorbell installation required. It is used for sound and light signaling. The doorbell (receiver) is plugged directly into a ~230V mains socket, and the transmitter is powered by an electromechanical converter and does not require the use of batteries. The learning system function allows you to log in additional buttons. The range of the bell in the open area is 200m. The receivers have 4-stage volume control and 36 polyphonic ringtones to choose from. ** Illustrative photos.