This electro-mechanical doorbell features a classic "ding dong" sound with an 85 dB volume. It is wall-mountable and uses a simple 2-wire installation. The doorbell can be powered by a 9v PP3 size battery (not included) or an 8v 1 amp transformer (not included). It can be used wired or wirelessly, with a wireless communication range of up to 30m in open space. Only ring buttons of the same series are compatible. Maximum transformer voltage is 12V.