Doorbells without batteries

 

— a kind of wireless bells with a receiving module powered by a standard 230 V household power supply. Inside the transmitter, such bells have a hidden mechanism with a piezoelectric element. By pressing it, there is a potential sufficient for the personal code of the call button to go on the air. The communication range of such devices often exceeds 100 m — they can be safely used not only in apartments, but also in private homes.