How Apartment Intercoms Work (and How to Automate Yours)

Most apartment intercoms are phone systems from the 1990s. Here's exactly how they work, why they haven't changed, and how to make yours smart in 2026.

The apartment intercom is one of the least-changed pieces of technology in urban housing. Most buildings use systems that were installed in the 1990s and work exactly the same way they did then. Understanding how they work helps explain both why they're frustrating and how to fix them.

The basic mechanism

A building intercom is essentially a phone system with a physical panel at the entrance. When someone presses a unit number (or finds a name on the directory), the system calls a phone number registered for that unit.

The resident answers the call. They hear the visitor or delivery person. If they want to let them in, they press a key on their phone — usually "9" — which sends a DTMF (Dual-Tone Multi-Frequency) tone back to the intercom. The intercom interprets that tone as "open the door" and releases the electric strike or magnetic lock on the entrance.

What "local area code" means

The intercom stores a phone number for each unit in a database maintained by the building management company. That number can be any working phone number — there's no technical requirement that it be a local area code. However, older intercom systems were designed when long-distance calls cost extra, and some legacy systems are programmed to only dial local numbers. Even modern buildings often have a preference for local area codes because it signals the resident is actually local.

In practice, you can give any number — but a local area code raises no questions.

Common intercom systems

• Aiphone — one of the most common in older buildings; uses a standard phone number
• Siedle — popular in higher-end buildings; phone-based
• DoorKing (DKS) — common in gated communities and larger apartment complexes
• Butterfly MX — modern cloud-based system with resident app; also supports phone number entry
• Latch — app-based with backup phone number option
• Comelit — European-origin, widely installed in US high-rises

BuzzBot works with any system that calls a phone number and accepts DTMF "9" to unlock. That covers nearly all of the above.

Why intercoms haven't changed

Intercom systems are infrastructure. Replacing them requires running new wiring, coordinating with building management, getting approval from the HOA or property owner, and paying for installation across every unit. Most buildings don't replace working systems until they break.

The phone-based model also has genuine advantages: it requires no app, no special hardware for residents, and works on any phone. The downside is that it requires a human on the other end to make decisions.

How to automate an existing intercom

Because the intercom just calls a phone number and listens for DTMF tones, you can automate it entirely by replacing the human with a programmed system. This is exactly what BuzzBot does:

• You give the building a BuzzBot phone number instead of your cell
• When the intercom calls, BuzzBot answers automatically
• BuzzBot runs through a verification flow: expected delivery → auto-buzz; known name → auto-buzz; uncertain → push notification to you
• DTMF "9" is sent programmatically when the verification passes
• Your real phone only receives the call if BuzzBot can't resolve it in 28 seconds

The intercom system doesn't know or care that it's talking to software instead of a person. From its perspective, a call was placed and DTMF "9" was received. Door opens.