Door entry systems and intercoms guide

Last reviewed: 2026-03-04

Which systems are affected

Some door entry systems and intercoms use the phone line to let you buzz visitors in. These are common in blocks of flats, sheltered housing, gated communities, and some commercial buildings. The visitor presses a button at the entrance, and the system calls your landline so you can speak to them and release the door.

If the system dials out over the traditional phone line (PSTN), it will be affected by the switch to digital voice.

Systems that are not affected include:

• Intercoms that use their own internal wiring (not the phone line)
• Video doorbells that connect via Wi-Fi (Ring, Nest, etc.)
• Systems that already use SIP or IP-based connections

How to tell if yours uses the phone line

Look at the entry panel or the control unit in the building's plant room. If there is a phone cable running from the system to a phone socket or telephone junction box, it uses the phone line. The installer's manual or the managing agent should be able to confirm.

In a block of flats, the system may be connected to a shared phone line or to individual residents' lines. Ask your managing agent or landlord which setup is in place.

What can go wrong

• Calls may not connect. The system may fail to reach your phone if the signalling is not compatible with digital voice.
• DTMF tones may not work. Many door entry systems use touch-tone signals (DTMF) to release the door lock. These tones can be unreliable over some digital voice connections.
• Power cuts. If the system routes through a broadband router, it will not work during a power cut.

What to do

1. Find out who is responsible. In a block of flats, the managing agent, freeholder, or housing association is usually responsible for communal door entry systems, not individual residents.
2. Contact the system installer or maintenance company. Ask them whether the system is compatible with digital voice and what changes are needed.
3. Test after migration. Once the phone line has been moved to digital voice, test the door entry system. Press the entry button and check that the call connects and the door release works.
4. Plan for replacement if needed. Some older systems will need to be replaced with IP-based or SIM-based alternatives. This is a capital expense that the building owner or managing agent should plan for.

For property managers and housing associations

If you manage a building with a phone-line door entry system, audit all entry systems now. Contact the installer for each building and get a written assessment of compatibility. Budget for replacements where needed. Lead times for new systems can be several months.

Residents should be told about any planned changes and given a timeline.

Gate and barrier intercoms

Some gated communities, car parks, and commercial premises use intercoms on gates or vehicle barriers that dial a phone number when a visitor presses the call button. These work in the same way as building door entry systems: the intercom calls your phone and you press a key to release the gate.

If the gate intercom dials over the traditional phone line, it is affected by the switch. The same risks apply: the call may not connect over digital voice, and DTMF tones for gate release may not work reliably. Contact the installer to check compatibility and plan for a SIM-based or IP-based replacement if needed.

What to ask the installer

When you contact the system installer or maintenance company, ask these questions:

• Is this system compatible with digital voice (VoIP)?
• Has it been tested on a digital voice line? If so, did the door release (DTMF) work reliably?
• If it is not compatible, what is the replacement? Is it IP-based or SIM-based?
• What is the cost and lead time for a replacement system?
• Will the replacement work in a power cut?