Portable Wireless digital Doorbell
Installation of a doorbell in an apartment : Portable Wireless Digital Doorbell
Quote from Article entitled Installation of a doorbell in an apartment:
The circuit of connection for different devices is different. As a rule, wires for the standard door unit are laid out in all new buildings. If you make repair by your own hands or connecting of a wire electric bell is not provided for any reason, then you can choose a product with any possible connection circuit, laying out wiring to it.
The full version of the article can be found here.