Doorbells are special signaling utilities. Their main function is to inform people inside the building about visitors. Doorbells are installed near the door or inside the door itself, depending on the type & design. All modern-day doorbells are actuated by an electric relay. Door viewers are supplementary visual aids that allow people inside the building to see and identify visitors. They are considered to have a bigger impact on safety because with the aid of viewers occupants are able to assess possible threat posed by unintended visitors. Door viewer can be installed in the door (a peephole), or in the doorbell panel, which may also contain a microphone. Such set-ups are commonly used by reception or guard staff on large industrial and commercial facilities. Mega Depot introduces a great variety of door viewers and doorbells, all for the lowest prices one can find.