This style of buzzer has remote video and a handset for sound, so the "buzz-in button" isn't directly connected to the door lock. The only external attachment is a header cable to board which connects the video, audio and door buzzer signals in series to other apartments.
Finding the door lock wires was a bit challenging. The model numbers listed on the parts led to some very vague schematics which suggested the door lock circuit would be a 12V supply which switched to ground to open the lock. This means the button was an NO or Normally Open style, so we'll see next we connect the ground and the 12V door open signal to the NO terminals on the wireless relay board. If you have trouble finding schematics, use a multimeter to find likely candidates and carefully play the guessing game by jumpering the terminals until the door opens. Make sure any circuit you close is between 5V and 24V DC to prevent a nasty surprise.
I used the multimeter to find a 12V signal and determined the yellow wire was the bingo, and obviously enough, the black wire was ground.
Wireless Relay Board
The relay board goes into the closet behind the door buzzer housing and is connected to the buzzer by fishing the wires through a small hole drilled in the back of the wall.
What? You don't keep a stash of shrink tube around? Bah. Use tape.
First we strip out about 4 inches of wire and separate the striped and solid ones to create positive and negative busses. We attach the appropriate banana plug to each group.
Then we strip away about 1/3 of the wire covering from the other side of the cable. Shrink tube the junction where the covering ends to prevent fraying. We shrink tube each pair of wires together to keep them from coming apart then attach alligator clips to their respective wires.
Make:NYC is having a name badge contest and I needed a badge to demonstrate at the first meeting.
I had some CrystalFontz Serial LCDs (Model CFA-632 $37) laying around and these neat little modules have a boot EEPROM that you can program to load text and graphics when power is applied to the module without serial data input.
I attached a voltage regulator for the power supply (battery eventually). I also connected the serial cable for programming. I then glued an "attractive" foam bezel to the front of the LCD.
This is the CrystalFontz boot programmer.
The finished product with lavish nylon string neck loop and 9v battery power source!
I should be able to cook up a halfway decent badge for the next meeting.
Now don't tell the co-op board, but I crafted a plan to ditch my Mul-T-Lock key for good. My apartment building, of course, uses an intercom system to remotely unlock the front door for guests, deliveries, etc. This keychain upgrade gets me in the front door... keylessly.
The mechanism is simple enough, just a momentary button on the panel in my apartment, but the mess of wires in the wall is a little unsettling. I took some meter readings of the terminals and sorted out the door button wiring. You can see where the door button is soldered through the PCB, which made it easier to identify the proper terminals. This panel has a "Door", "Talk" and "Listen" button. The "Door" button is normally-open and the circuit is about 22V. In the following steps we're going to effectively bypass the button with our own circuit.
I purchased a relatively cheap RF relay kit from Carl's Electronics. The HD2Combo 2-channel RF relay kit. These things are fun and just $30, get one even if you don't think you'll ever use it. Don't forget a 12V supply for the board. This is a rolling code transmitter, so no -- not just anyone with a remote can activate the relay.
Okay so, kit and intercom meet. I connected one of the normally-open relay circuits on the RF board in parallel to the "Door" button with wires marked "To Relay" and "From Door" in the photos above. This configuration allows either the relay or the button to operate the door. If your particular application uses a normally-closed circuit to open the door, wire the button in series and connect it to the normally-closed circuit on your relay.
Also show in the above photo are the 12v DC supply wires (black) and the antenna wire (also black).
My apartment is actually directly over the building entry, so range on the transmitter fob is not nearly an issue. I can activate the relay from my bedroom or from in front of the building. It's not the most impressive hack, but it sure makes my life easier.
And there you go. A keyless entry. So what's the second button do? Nothing. At least, not yet.
TODO: Hide the receiver and wire.
This is one of those things where I might caution that you not try at home unless you're very snuggly with your landlord.