How Apartment Buzzers Work: Panel, Phone Line, Unlock

Most apartment buzzers are telephones in disguise. A visitor presses your name or unit code on the entry panel. The panel dials a phone number stored next to that code. Your phone rings, you talk through the panel's speaker, and when you press a key — usually 9 or 6 — that tone travels back down the line and releases the door lock. That's the whole system.

Once you see it that way, almost everything confusing about buzzers starts to make sense: why the panel "calls" you, why the unlock key is a number, why nothing works when your phone is on silent, and why your building can point the buzzer at a different number without touching a single wire.

What actually happens when someone presses your buzzer?

Here's the full path, step by step. Picture it as a straight line from the sidewalk to your door lock.

1. The panel. Your visitor walks up to the box at the entrance — a call box, a directory panel, a keypad with a tiny speaker. They scroll to your name or punch in your unit's directory code (not your apartment number, usually a separate three- or four-digit code). This is the part people mean when they ask about a "buzz code."

2. The lookup. Inside that panel is a small programmed database. Each directory code is mapped to one phone number. When the visitor presses your code, the panel looks up your number. Nothing personal is stored there — just a code and a number.

3. The dial-out. The panel picks up a phone line and dials. That line might be an old copper landline, a VoIP line the building pays for, or in newer systems a cellular module. Either way, it's placing a real phone call.

4. Your phone rings. You answer. The panel's microphone and speaker become a hands-free intercom. Audio quality is often rough because these speakers live outdoors and get rained on for a decade.

5. The unlock tone. You press 9 (or 6, or 0 — it depends on how the building programmed it). Your phone plays a specific dual-tone beep. The panel is listening for exactly that beep.

6. The electric strike. When the panel hears the right tone, it closes a relay. That relay sends power to an electric strike or magnetic lock in the door frame. The latch releases for a few seconds. The visitor pulls the door. Call ends.

That's it. Six steps, and five of them are just a phone call.

Why is the unlock button a number key?

Because the panel can't see your screen. It can only hear sound.

When you press a key on any phone, it generates a DTMF tone — Dual-Tone Multi-Frequency. Each key plays two pure tones at once, one from a low group and one from a high group. Press 9 and you get 852 Hz plus 1477 Hz layered together. That pairing is deliberate: no human voice or background noise naturally produces two clean frequencies at those exact pitches simultaneously, so a machine listening on a phone line can pick it out reliably.

Those are the same tones behind "press 1 for billing." Your buzzer panel is running the world's simplest phone menu, and the only option is "open the door."

This is also why a mis-programmed unlock digit is so common. If maintenance set the panel to accept 6 and everyone in the building has been told 9, you'll hear the visitor fine and the door will simply never open. It's worth confirming your building's actual unlock digit with your property manager rather than guessing.

How does an intercom system work compared to a buzzer?

People use the words interchangeably, but there's a real distinction worth knowing.

A true intercom is a closed, wired system. Dedicated wiring runs from the entry panel to a handset mounted on your kitchen wall. Nothing touches the public phone network. You pick up the handset, talk, and press a button on that handset to unlock. Older buildings — especially pre-1990s walk-ups — often have these. Brands like TekTone show up here constantly.

A telephone-entry buzzer replaces all that wiring with a single phone line at the panel. Instead of running cable to 60 units, the building runs one line and programs 60 phone numbers. Cheaper to install, far easier to update, and it works whether you're in the shower or three states away.

Most North American buildings built or renovated in the last thirty years use the telephone-entry approach. That's why your buzzer probably calls your cell phone — or could, if the number were updated. If you want the deeper version of this comparison, our page on apartment call boxes walks through the common panel types.

Why do buzzers fail so often if the design is this simple?

Because every link in the chain is a single point of failure, and most of them are decades old.

The most common problem is the phone number itself. The panel dials whatever number was programmed when the unit was last leased. If that's a disconnected landline or a previous tenant's cell, your visitor gets a dead ring while standing in the cold.

And landlines are disappearing fast. According to the CDC's National Center for Health Statistics, 75.2% of American adults lived in wireless-only households — no landline at all — in the July–December 2023 National Health Interview Survey. Millions of buzzer panels are still dialing numbers that stopped existing years ago. If that's your situation, our guide to getting buzzed in without a landline covers the fixes.

Other failure points: the panel speaker corrodes and audio turns to mush. The directory sticker fades until nobody can find your name. You're in a meeting, on a plane, or the number lands in spam filtering. Or you simply don't answer in the eight seconds a delivery driver is willing to wait — and the package goes back on the truck.

Can a buzzer let people in without you answering?

Yes, and this is where the phone-call design becomes an advantage instead of a liability.

Because the panel just dials a number, that number doesn't have to be a person. It can be a service that answers on your behalf. That's how Enterkey works: you get a unique virtual phone number, ask your property manager to point your unit's buzzer at it, and from then on your phone app decides what happens when someone buzzes. No hardware, no rewiring, no wall panel. Property managers usually make the change within a day. Here's the full walkthrough.

From there you can set a timed key — five minutes to twelve hours, or Forever with a required PIN — and while it's active Enterkey answers the buzz and sends the unlock tone automatically. Nobody has to be home. You can also give visitors a PIN to type or speak at the panel, set recurring weekly unlock windows, share access with roommates by invite link, or just have the buzz forwarded to your phone like normal when no key is running.

A few honest limits. Enterkey is iOS only right now — no Android app. It works with any buzzer that dials out to a phone number, but if your building uses a true intercom hardwired to a handset in your unit, there's no phone number to redirect and it won't work. And you do need your property manager to make that one small change; you can't do it from the app alone. Plans are $9.99/month or $69.99/year, and the details are on our pricing page.

If your buzzer keeps failing at the exact moment it matters — a delivery, a friend at the door, a contractor you scheduled — Enterkey is worth trying, because it turns that eight-second phone call into something that just happens whether you're free or not. New members get their first month free, and you can cancel before it ends and pay nothing. Questions about whether your panel is compatible? Email support@enterkey.app; real people usually reply within hours.