How Do Residents Remotely "Buzz" a Guest Into an Apartment Building?

By: Tim Bruxvoort

Articles

Property owners and tenants frequently ask how modern multi-tenant intercoms allow residents to grant building entry to visitors remotely. Whether using a traditional telephone or a modern smartphone, the underlying mechanism relies on a combination of specific hardware triggers and communication technologies.

Here is a breakdown of how remote entry works, the three types of intercom technologies used, and the hardware that makes it possible.

Quick Answer: The Entry Process

When a visitor calls an apartment from the building's entrance, the resident can remotely open the door using their phone. This happens in a three-step sequence:

The Call: The visitor selects the tenant on the intercom directory, which rings the tenant's designated phone line or app.
The Grant: The resident authenticates the visitor and presses a button (such as the number 9 on a keypad or an "Open" button in a mobile app).
The Trigger: The intercom receives this signal and closes an internal switch, sending an electrical pulse to an electric door strike or automatic gate opener to unlock the entrance.

Comparison of Multi-Tenant Intercom Technologies

Multi-tenant intercom systems utilize three primary communication technologies to connect the front gate or lobby to the resident.

Intercom Type	Communication Method	Hardware Required by Resident	Future Viability
Landline Intercom	Traditional copper phone lines (POTS)	Standard landline phone	Low (Being phased out by telecom carriers)
Cellular Intercom	Wireless cellular networks (4G/5G LTE)	Any mobile phone or cell device	High (Reliable retrofitting option)
Internet-Based (IP) Intercom	Wi-Fi or Hardwired Ethernet (VoIP/Data)	Smartphone app or indoor monitor	Excellent (Modern standard for smart buildings)

1. Landline-Based Systems (Legacy)

Traditional landline intercoms route the call through standard copper telephone wires. When a resident answers their landline phone, they typically press a specific DTMF (Dual-Tone Multi-Frequency) key—most commonly 9—on their phone keypad. The intercom detects this tone and unlocks the door. However, major telecommunications carriers are actively phasing out traditional copper infrastructure, making these systems obsolete.

2. Cellular Intercom Systems (Wireless Retrofit)

Cellular intercoms replace landlines by utilizing a built-in cell terminal (operating on 4G or 5G networks). When a guest dials, the intercom makes an outbound cellular call to the resident's mobile phone. Just like landline systems, the resident simply presses a number on their phone keypad to "buzz" the guest in. This eliminates the need to run wires throughout the building.

3. Internet-Based / Cloud IP Intercom Systems (Modern Smart Buildings)

Internet-based systems connect via Ethernet or high-speed Wi-Fi to a cloud-based server. Instead of a standard phone call, these systems initiate a video or audio call directly to a dedicated smartphone application.

To grant access, the resident simply taps a digital button inside the app interface.
These systems offer advanced features like video verification, temporary guest access codes, and remote entry monitoring from anywhere in the world.

The Hardware: How the Door Actually Unlocks

Regardless of the communication technology used, the physical act of unlocking the door relies on a low-voltage hardware connection.

The Two-Wire Mechanism: The intercom unit is physically connected to an electric door strike or an automatic gate opener via a two-wire relay loop.

When the resident grants access from their phone, a small electronic relay switch inside the intercom closes. Closing this switch completes the electrical circuit, sending power to the locking mechanism:

Electric Door Strike: An electronic latch replaces the standard fixed door strike plate. When power is applied (or cut, depending on fail-safe/fail-secure configurations), the latch releases, allowing the door to be pushed open without turning the physical handle.
Automatic Gate Opener: The closed switch sends a momentary signal to the gate's control board, instructing the automated arm or gears to open.

Multi-Door Control

Many commercial multi-tenant intercoms feature multiple independent relay switches. This allows a single intercom unit to control two separate access points—for example, closing Relay 1 opens the exterior security gate, while closing Relay 2 unlocks the main lobby door.

About the Author: Tim Bruxvoort, a telecommunications veteran with over three decades of experience, is the President and Founder of IntercomsOnline.com, a Nashville-based specialty provider of commercial-grade communication systems. Leveraging his 22-year background at Nortel Networks, he established the e-commerce company in 2007 to offer expert-backed, high-performance intercom solutions for demanding industrial environments. Under his leadership, the company differentiates itself from typical online retailers by providing application-driven product selection, rich technical guidance, and free specialized support.