Security systems design

WHAT IT IS

Security systems design covers access control, intruder detection and video surveillance as one system rather than three separate procurements: what is controlled, what is detected, what is recorded, and how those decisions interact with the way people are meant to leave the building.

The interface with life safety is the part that goes wrong. Every access-controlled door on an escape route needs a fail-safe release on fire alarm and a mechanical means of escape that does not depend on the electronic system working. That is a design decision at Stage 3, not a commissioning discovery at Stage 5.

WHEN YOU NEED IT

On any building with controlled access — offices, schools, banking and retail, laboratories, plant and switch rooms — and on any refurbishment where the door schedule, the escape strategy or the occupier's operating model changes.

Also where a system already exists and is being extended: the head end, the credential technology and the cabling standard have to be established before new devices are specified against them.

OUR PROCESS

Zoning first. Who goes where, at what times, and what happens when the system fails — those three answers set the door schedule, the reader count and the containment. Device selection comes afterwards.

Video surveillance is designed against an operational requirement in the terms of BS EN 62676-4: what each camera is for — monitor, detect, observe, recognise, identify — because that determines the pixel density on target, and therefore the lens, the position and the number of cameras. A camera specified without one is a camera that produces footage nobody can use.

DELIVERABLES

What you receive

Security zoning strategy and door schedule
Access control device layouts and containment
Intruder detection layouts and grading
Camera layouts against a stated operational requirement
Interface schedule with fire alarm and door release
Head end, network and power requirements

STANDARDS

Standards applied

The editions in force at the time of design. Where a standard is amended mid-project we confirm which edition the appointment is based on.

BS 7671:2018+A4:2026Requirements for Electrical InstallationsIET
BS EN 50131Alarm systems — intrusion and hold-up systemsBSI
BS 8243:2021Design, installation and configuration of intruder and hold-up alarm systems designed to generate confirmed alarm conditionsBSI
BS EN 62676-4:2015Video surveillance systems for use in security applications — application guidelinesBSI
BS EN 60839-11-1:2013Alarm and electronic security systems — electronic access control systemsBSI
BS 7273-4:2015+A1:2022Actuation of release mechanisms for doorsBSI
Approved Document BFire safety (England)GOV.UK
Technical Handbook Section 2Fire (Scotland)Scottish Government

QUESTIONS

Common questions

How do access controlled doors work with the fire alarm?

Doors on escape routes must release on fire alarm activation, and BS 7273-4:2015+A1:2022 sets out the actuation categories and the level of reliability required for each. Fail-safe locking, an emergency door release adjacent to the door, and a mechanical override that works with no power are all designed in, so escape does not depend on the access control system operating.

What is an operational requirement for CCTV?

A written statement of what each camera has to achieve — monitor, detect, observe, recognise or identify — expressed as pixels per metre on the target, following BS EN 62676-4. It is agreed with the client before cameras are specified, because it determines lens, mounting position, lighting and camera count. Without it, coverage is guesswork.

What intruder alarm grade does a building need?

Grade is set by a risk assessment under BS EN 50131-1, from Grade 1 for low risk to Grade 4 for high risk premises. Most commercial buildings sit at Grade 2 or 3. Where police response is required, the system must generate confirmed alarms in accordance with BS 8243 and be installed by a company certificated to the relevant scheme.