Wireless Doorbell Camera
Installation of a doorbell in an apartment : Wireless Doorbell Camera
Quote from Article entitled Installation of a doorbell in an apartment:
If all wires have already been laid in an apartment, doorbell installation will not take much time. The device operates from electricity, so you need to follow safety rules when using electrical appliances. Connection of electrical products is carried out only after power has been turned off in the entire apartment.
The full version of the article can be found here.