An ESP32-Powered Fix for a Dead Intercom

Building a DIY solution to every problem may come naturally to many Hackster News readers, but there is a certain convenience that comes with buying a prebuilt, commercial product. There is no time spent researching the perfect components or frustration when things aren’t working as expected. Just plug it in and you’re good to go. But if that product relies on external resources that the manufacturer suddenly decides to take away, you’re out of luck.

A friend of Jack Hogan recently ran into a similar situation when apartment management failed to renew the intercom’s cellular service. This meant that when visitors looked him up in the directory, it could no longer call him to open the front door and let them in. Upset with having the rug pulled out from under him, this friend asked Hogan for help.

After inspecting the system, Hogan and a collaborator found that they were dealing with a DoorKing 1834-080 intercom paired with a voice control unit and an exposed networking router. Initial attempts focused on gaining control through the router itself, which still used default credentials (of course!) and even allowed configuration downloads containing sensitive password fields. While this revealed glaring security oversights, leveraging the router would have required reverse-engineering proprietary communication protocols — no thanks!

A second idea involved emulating phone signals through the system’s analog lines, since the intercom previously relied on DTMF tones to unlock the door. But without clear insight into how the controller validated calls, this path was equally uncertain.

So instead of trying to control the system from the top down, they explored the physical infrastructure. Inside a junction box, they uncovered direct wiring to the gate’s solenoid — the simple electromagnetic mechanism responsible for locking and unlocking the door. Unlike the higher-level systems, this component required no authentication: apply power, and the gate opens.

From there, the solution became straightforward. They inserted a relay — controlled by an ESP32 microcontroller — inline with the solenoid wiring. The relay allowed the original system to function normally while enabling independent control when triggered. Power was sourced from the intercom’s AC supply using a rectifying regulator.

On the software side, the device was programmed in Rust and integrated with Apple Home via the Matter protocol. This allowed the resident to unlock the gate remotely or automate access for guests using a familiar smart home interface. Safeguards were included to ensure the gate would only remain unlocked briefly.

This solution may not exactly please apartment management, but it is a clever way to address a problem that they have not been willing to fix.