Modern Video Door Phone
Installation of a doorbell in an apartment : Modern Video Door Phone
Quote from Article entitled Installation of a doorbell in an apartment:
Selection of the electrical device depends on whether you install in an apartment or in a house. They may have two or four wires. Voltage 110V (220V) is needed for a 2-wire button, and for a 4-wire button - 5V. Both types can be installed in an apartment. And in a house where the button and the wire are affected by the weather conditions (rain, snow, high humidity) only 4-wire devices are installed.
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