Alright, if you're dealing with building security and need a solid intercom system, this Aiphone IE-2AD master handset is worth considering. This thing is the main control unit that works with door intercoms and sub-master handsets (sold separately, just FYI). Basically, when someone shows up at your door and uses the intercom, this handset rings with this adjustable chime tone and a little LED lights up. You can talk to them privately through the handset, and if you want to let them in, there's a door release button that works with an electric strike lock. It can handle up to two different doors and up to two additional sub-master handsets, so you can cover multiple entrances or different rooms in a larger building. The technical specs: door release can handle 24V at 500mA, maximum distance from master to door is 500 feet with 22 AWG wire (or up to 1,180 feet with thicker 18 AWG wire), and it needs 12-16VAC power. Aiphone has been making these systems since 1948, so they know what they're doing. Comes with the mounting bracket and hardware. Pretty straightforward system for small to medium buildings that need basic access control without going overboard.