Controlling old-school apartment entrance buzzer / intercom

Since getting into SmartThings recently, I had been searching for a way to unlock the outside entrance with my phone so I could let delivery folks, cleaners, and friends in when I wasn’t at home.

Thankfully, I was able to do so after reading a couple of helpful posts online, and tweaking them to my situation. Posting here in case others with similar intercom systems are looking to do this in the future.

My intercom system consists of the VC-K phone upstairs and a VC-M unit at the main entrance (photos below). Guests press a button on the VC-M and the VC-K “buzzes”. The resident can press a button on the VC-K to unlock the door downstairs and let guests in.

Thankfully, I came across a post written by a user, Jamie, here that explained the VC-K wiring:

The entire system runs on 12V DC power with low current…I have access to the VC-K unit in my apartment… Terminals 1 and 2 provide communication with the front door. Terminal 3 is ground. Terminal 4 carries 12V and when connected to ground will unlock the door… Terminal B drives the buzzer in the handset – its inactive state is 0v, but will send 12V when someone is pressing the buzzer for my unit at the front door.

So all I needed to do was connect terminals 3 and 4 in the VC-K with a Z-wave relay switch to remotely open the main entrance door.

Following the footsteps of Smartthings user Paul here, I went ahead and purchased the Linear relay FS20Z-1.

I placed the relay into a surface-mount single gang box that I stuck on the wall. Then, I got some wiring, opened up the VC-K and hooked up the wire to terminals 3 & 4, and put the VC-K back on. Ran the wires to the load terminals of the relay. Lastly to power the relay - I got an old computer cable, which I connected to the power and neutral terminals of the relay and plugged it in to a 120V wall socket.

Things worked fine at this point, but I didn’t want the relay switch to stay on permanently when switched on - I only wanted it on for a brief moment to let someone in, and then switch off automatically. As another user mentioned I went to the Smartthings IDE, and then “manage my devices” where I edited the relay to be a “Z-Wave Virtual Momentary” switch.

Now, when I turn on the relay switch, it unlocks the main apartment door for a couple of seconds, and goes back to being locked. Success!


any chance to hook it up to the buzzer part. When someone hits the buzzer it can flash the lights in the house?