An intruder alarm is only as good as its blind spots. A PIR aimed across a sofa, a contact missing from the patio door, a hallway the beam never sweeps - any of them turns a tidy spec sheet into a real vulnerability. This guide walks through planning an intruder alarm layout on a floor plan with RoomPlot, including the one thing most tools cannot do: showing where each detector actually sees.
The devices an intruder system needs
RoomPlot ships a 50-item Security Alarm symbol library, so you can lay out the whole system to a recognised standard. The core pieces:
- Control panel and keypad - the brain and the user interface, usually near the main entry and a discreet utility space.
- PIR and dual-tech detectors - the movement sensors that cover each protected room, including pet-immune versions for occupied homes.
- Door and window contacts - perimeter protection on every accessible opening.
- Sounders, strobes and a bell box - internal and external warning devices.
- Beam and glass-break detectors - for long runs, conservatories and large glazed elevations.
Coverage you can actually see
Place a PIR and RoomPlot draws its field of view as a cone, then clips that cone against the walls. It is a true visibility calculation: the sensor only covers the part of the room it can see, and blind spots behind corners and furniture update live as you rotate or move the device. A motion detector defaults to a 90 degree by 12 m cone, and you can edit the field of view from 10 to 360 degrees and the range from 1 to 40 m. Aim it by rotating the symbol on the canvas.
Lay out the system step by step
- Capture the property. Scan or draw each floor so room shapes and openings are correct.
- Protect the perimeter first. Add a contact to every external door and accessible window, then a bell box high on the front elevation.
- Cover the volumes. Place a PIR in each room, aim the cone into the space, and nudge it until the blind spots fall on low-value corners, not on the route to the safe or the back door.
- Set the colours and grade. Override a device colour where two systems share a plan, and label zones so the engineer commissioning it can follow your intent.
Tip. Walk the finished plan as if you were the intruder. If you can trace a path from any opening to a target room without crossing a blue cone, you have found a gap a survey would have missed.
Hand over a plan, not a promise
When the layout is right, export it. The single-page plan drops straight into a quote, and the multi-page report adds a cover page, the symbol legend and the coverage overlay for a professional proposal. Pair it with our guide to the CCTV camera coverage plan when a job needs both intruder and surveillance on the same drawing.
Win the job on coverage
Clients buy certainty. A plan that shows exactly where every sensor sees, with no hand-waving about blind spots, closes more surveys than a parts list ever will. Explore the full set of RoomPlot guides to take your security designs from site visit to signed contract.
