Door Entry Systems: Audio vs Video, IP-Based Intercoms, Electric Strikes vs Mag Locks and Fire Release

Quick Answer: Door entry systems range from simple audio intercoms with an electric strike to IP-based video systems integrated with access control and mobile apps. The critical installation decision is locking hardware: electric strikes or mag locks on fire exits must be fail-safe (open on power loss) under the Regulatory Reform (Fire Safety) Order 2005. Video intercom quality for identification requires a minimum of 100 pixels per metre of face width — equivalent to a 2 MP camera at 2–3 m range with a standard lens.

Summary

Door entry systems (also called door intercoms or video door phones) are one of the most common security product installations in the residential and commercial market. They range from a simple audio-only unit with a door bell press and electric strike on a flat block entrance, to a full IP video intercom integrated with smartphone apps, access control databases, and cloud recording.

The technology has changed dramatically in the last decade. Traditional systems used dedicated 2-wire or 4-wire analogue wiring between outdoor station and indoor monitor. Modern IP-based systems run over Cat6 Ethernet, support PoE, integrate with VMS software, and allow remote door release from a smartphone anywhere in the world.

Despite the technology shift, the fundamental installation requirements remain the same: the outdoor station must withstand the elements, the locking hardware must be appropriate for the door type and fire designation, and the cabling must be routed cleanly and protected from tampering.

Key Facts

• Audio intercom — press-to-talk communication only; no video; lower cost; suitable for low-risk residential
• Video intercom — camera at outdoor station with monitor or app display indoors; required where visual identification is needed
• Analogue 2-wire — legacy residential system; combined audio/power on one pair; limited distance without amplifier; typically BUS-based with multiple handsets from one riser cable
• Analogue 4-wire — separate audio and video pairs; higher quality; common in residential blocks
• IP intercom — connects via Ethernet/PoE; integrates with network video recorders; remote access via smartphone; scalable to enterprise
• SIP protocol — some IP intercoms use SIP to connect to IP-PBX phone systems or mobile apps; flexible but requires SIP server configuration
• Electric strike — surface or mortise-mount release unit; available fail-safe or fail-secure; low power draw; most common for residential intercoms
• Magnetic lock (maglock) — holding force 280–560 kg; fail-safe by nature; requires continuous power to hold locked; preferred for high-traffic entrances
• Electric bolt — fail-secure; slides into a keep in the door frame; high security; not for fire exits
• IP66 or IP55 rating — minimum for outdoor station; IP66 (dust-tight, water jet resistant) preferred for exposed locations
• IK08 rating — recommended for vandal resistance on outdoor stations in public areas
• PoE (Power over Ethernet) — IEEE 802.3af (15.4 W) or 802.3at (30 W); powers IP intercom stations and many electric strikes without separate PSU
• Fire release — electric locking on fire exits must release on fire alarm activation via dry contact; mandatory under RR(FS)O 2005
• Break glass unit — manual override on secure side of access-controlled fire exit; allows exit without credentials or network
• GDPR — video door entry systems that capture identifiable images are subject to UK GDPR; privacy notice required for visitors
• BS EN 50133 — access control standard referenced for door entry integration; BS EN 60839 series for integrated systems

Quick Reference Table

Detailed Guidance

Analogue vs IP: Which System to Specify

Analogue 2-wire BUS systems are still widely installed in residential blocks because:

• A single pair of cables runs up each riser, branching to each flat
• Adds/removes of handsets are simple
• No network infrastructure required
• Proven 20+ year lifespan with major brands (Urmet, Comelit, Videx, Fermax)

Limitations of analogue systems:

• Video quality is SD (typically 380–420 TVL)
• Limited smartphone integration
• Number of outdoor stations on one BUS is restricted (manufacturer dependent — typically 4–8)
• Difficult to integrate with modern access control

IP-based intercoms are appropriate when:

• High-definition video is required for identification (public authority, high-security commercial)
• Remote access via smartphone is a customer requirement
• Integration with VMS (video management software) for recording is needed
• Multiple entrances need to appear at a single reception point
• The building already has Cat6 infrastructure

IP intercoms require:

• PoE switch or PoE injector at each outdoor station
• Fixed IP address or DHCP reservation for each device
• Firewall/router configuration for remote access (port forwarding or VPN — avoid port forwarding for security)
• SIP server if using SIP protocol integration

Electric Strike Installation

The electric strike replaces the mechanical strike plate in the door frame. The lock bolt passes into the strike and the strike's keeper arm can be electronically retracted to release the door.

Installation checklist:

1. Verify fail state — read the part number; fail-safe and fail-secure variants look identical; label on the box
2. Check door frame compatibility — standard mortise latch works with most strikes; deadbolt-operated strikes need a specific product
3. Power supply voltage — strikes typically 12 V DC or 24 V DC; match to PSU output exactly
4. Current draw — most strikes draw 0.2–0.5 A holding; size PSU and cable accordingly
5. Rectifier — on AC-powered systems, fit a suppression diode across the strike to protect the releasing relay from back-EMF
6. Strike monitoring — some strikes have a microswitch monitoring bolt position; wire to panel for door-open fault detection
7. Door hardware — the latch must be spring-loaded (not deadlocking) for the strike to work; confirm with door hardware supplier

Magnetic Lock Installation

Maglocks offer higher holding force and are more resistant to forced entry than standard electric strikes. They are inherently fail-safe.

Installation points:

• Armature alignment — the armature plate on the door face must align precisely with the maglock body on the frame; use the supplied alignment kit
• Door gaps — maximum 3 mm gap between armature and maglock body; beyond this, holding force drops significantly
• Power requirement — typically 0.5 A at 12 V (6 W) for 280 kg lock; size PSU accordingly plus 20% margin
• Weatherproofing — external maglocks need a cover hood; condensation on armature reduces holding force
• Remanence delay — some maglocks have a brief residual magnetism after power-off; allow 100–200 ms release delay in timed outputs
• Door speed — high-traffic swing doors hit the armature with force; consider a door closer with controlled speed

Fire Release Wiring

Every access-controlled or intercom-operated door on a fire escape route or means of escape requires automatic release on fire alarm activation.

Wiring method:

1. The fire alarm panel has a dedicated door-release output (volt-free relay contact, normally closed)
2. On fire alarm, the relay opens, de-energising the lock release circuit
3. Fail-safe locks open; fail-secure locks stay locked (which is why fail-secure cannot be used on fire exits)
4. A break glass unit (green "Push to Exit") is wired on the secure side in series with the release circuit for manual override

The fire alarm panel output must be:

• A volt-free contact (not an active output from an alarm panel that may share ground with the access system)
• Tested at commissioning to confirm all fire exit locks release
• Labelled on the fire alarm panel cause-and-effect schedule

Note: BS 9999:2017 requires that locks on escape routes can be opened from the escape side without a key and without special knowledge. The break glass unit satisfies this if it is visible, accessible (no obstructions), and clearly labelled "PUSH TO EXIT."

IP Video Quality for Identification

For a video intercom to be useful for identifying callers, the image quality must be sufficient. Use the same pixels per metre rule as CCTV:

• Recognition (can identify known person): 250 px/m
• Identification (can identify unknown person from image): 500 px/m
• Face close-up at 2 MP with a standard lens at 1.5 m range typically provides 400–600 px/m — adequate for identification

Wide-angle lenses give a broader view of the approach but reduce face resolution. For residential doors where you only need recognition, a 130° lens at 1 m is fine. For high-security reception where precise identification is needed, use a narrower angle to fill the frame with the face.

Frequently Asked Questions

Can I fit a video intercom to a tenant's flat and link it to their smartphone?

Yes. Most modern residential video intercom systems have companion apps (Comelit, 2N, Doorbird, Ring, etc.) that relay calls to smartphones. The installers configure the cloud account or SIP credentials during commissioning. Note that cloud-relayed systems require ongoing internet connectivity and the cloud service to remain operational — discuss with customers who have data privacy concerns about cloud services.

What is the maximum cable run for an analogue 2-wire intercom?

Manufacturers specify this differently, but a practical guide for major brands is 200–300 m on 0.75 mm² twisted pair, with the total resistance of the BUS below the manufacturer's threshold. Beyond this, signal amplifiers or repeaters are available. Always check the specific manufacturer's wiring guide — exceeding the run causes poor audio or video.

Does a video intercom require ICO registration under GDPR?

If the video intercom captures images of identifiable individuals (visitors, delivery drivers), the operator is processing personal data. Organisations (not sole traders at their own home) should include the door entry system in their records of processing activities. A privacy notice should be displayed at the door station. Most domestic residential users are exempt under the "household exemption" in UK GDPR, but blocks of flats managed by a residents' association or management company are not exempt.

What is the difference between a door entry system and an access control system?

Door entry systems are visitor identification and communication systems — a visitor presses a button, the resident identifies them via audio/video, and presses a release button. Access control systems manage credentials (cards, fobs, PINs) for authorised users who do not need to press a button. Many modern systems combine both: residents use credentials for direct entry; visitors use the intercom. See access control systems guide for the access control side.

Can I use a PoE switch output directly to power an electric strike?

Not directly from the PoE data port. However, many PoE intercoms have a relay output that switches 12 V/24 V DC from a local PSU to power the strike. Some IP intercoms have an integrated strike power supply. Always check the wiring diagram — never connect an electric strike to the data pair of a Cat6 cable.

Regulations & Standards

• Regulatory Reform (Fire Safety) Order 2005 — requires fire exits to be openable without keys; governs fail-safe requirements for electric locking on escape routes

• BS 9999:2017 — Code of practice for fire safety in the design of buildings; Section 18 covers electromechanical locking

• BS EN 60839-11-1:2013 — Electronic access control systems; applies to integrated door entry/access systems

• BS 8220:2000 — Guide for security of buildings against crime; door entry guidance

• UK GDPR / Data Protection Act 2018 — governs video recording at door entry points

• BS EN 50133-1:2002 — Alarm systems; access control systems for use in security applications; system requirements (referenced for integrated systems)

• IEEE 802.3af/at — PoE standards relevant to IP intercom power delivery

• 2N IP Intercom Technical Guide — Comprehensive IP intercom installation documentation

• Comelit Group Technical Resources — Analogue and IP door entry systems

• BSIA Door Entry Systems Code of Practice — Industry guidance on door entry systems

• ICO CCTV Guidance — Relevant GDPR guidance applicable to door entry video

• Videx Security Technical Documentation — UK manufacturer technical installation guides

• access control systems guide — Credentials and access control integrated with door entry

• cable installation security systems — Cabling for door entry and intercom systems

• security system commissioning — Commissioning door entry systems

• gdpr cctv ico obligations — GDPR obligations for video capture at door entry points

• cctv camera types selection — Camera selection for video intercom identification quality