A home needs enough intrusion detection devices to monitor the selected doors, windows, interior movement, and exterior approaches in its security plan. Count protected openings, then add motion and glass break coverage where needed. Photo verification changes a detector's capabilities; outdoor detection may add devices. Square footage alone cannot establish the total.
This guide focuses on intrusion detection devices. Smoke, carbon monoxide, water leak, and other life-safety or environmental detectors should be planned separately for the property and applicable requirements.
How Do You Count Door and Window Sensors?
List openings to monitor: front, rear, patio, and side doors, including the door between an attached garage and the house.
A contact sensor detects opening through the separation of a magnet and detector. Ajax DoorProtect Jeweller is designed for door and window opening detection.
For a conventional layout, plan a separate contact for each independently moving section whose opening must be detected. One window assembly may have several operable sections.
Prioritize accessible windows, including those reachable from patios, balconies, roofs, or other structures. An upstairs window is not automatically inaccessible. A fixed pane cannot be monitored for opening, so if that glass needs intrusion detection, it requires a different detection method.
An overhead garage door needs a separate assessment of movement, construction, environment, and suitable equipment.
How Many Motion Detectors Do You Need?
Count the interior areas or routes needing movement detection, such as hallways, living areas, and paths beyond entry points.
Rooms, partitions, and furniture can create gaps requiring another detector or position. Published maximum range does not establish coverage throughout a floor.
Ajax MotionProtect Jeweller provides indoor motion detection. Final placement must follow the selected model's instructions and be checked with a detection-zone test.
Review pets' routes and elevated surfaces when placing detectors. Our Ajax motion detector pet immunity guide explains the testing requirements.
Do MotionCam Detectors Change the Sensor Count?
Ajax MotionCam Jeweller detects motion and can provide alarm photos for visual context when the compatible system is configured for photo verification. Count it as one detector, not a motion detector plus a separate camera.
Choose motion-only detection or motion with visual verification according to the zone's needs. If Ajax MotionCam Jeweller is selected instead of a motion-only detector for the same tested zone, it still counts as one physical detector. Alarm photos do not replace continuous surveillance video.
When Do You Need Glass Break Detection?
Glass break detection addresses an event that an opening contact alone does not detect: glass breaking while the protected sash or door remains closed.
An acoustic detector may monitor several suitable panes when they fall within its supported coverage and sound can reach the microphone.
The Ajax GlassProtect Jeweller manual warns that curtains can muffle sound. Check glass suitability, positioning, distance, partitions, and coverings, then follow the manufacturer's test procedure.
Ajax CombiProtect Jeweller combines motion and glass break detection. Count it once when its location meets both functions' placement and testing requirements.
Glass with applied film needs another approach. Ajax GlassProtect Jeweller and Ajax CombiProtect Jeweller do not detect breaking glass covered with protective, sun-control, decorative, or other film.
How Do Outdoor Detectors Affect the Sensor Count?
Outdoor detection is an additional layer that not every home needs. Add it for a defined objective, such as detecting a person approaching a door through a side passage, gate, patio, driveway, or route beside windows.
Depending on the objective, a design may use Ajax MotionProtect Outdoor Jeweller for motion, Ajax MotionCam Outdoor Jeweller for motion with alarm photos, or Ajax Curtain Outdoor Jeweller for a narrow detection zone.
Count devices by layout, approach routes, detection objective, and tested coverage. Keep routine activity outside the intended alarm zone. See our guide to Ajax outdoor and perimeter security design for detailed planning.
What Does a Sample Sensor Count Look Like?
For illustration, assume three doors and six independently opening window sections need contacts, two interior areas need separate motion detection, and suitable living-room glass without applied film needs acoustic detection.
Outdoor perimeter detectors are not included in this 12-device example. A property that requires driveway, side-yard, gate, patio, or other exterior approach detection may need additional devices.
This is an illustrative count, not a universal package. It excludes the hub, keypad, sirens, cameras, and safety or environmental detectors.
Does Nighttime Use Change the Coverage Plan?
Yes. Interior motion detection may be unsuitable along a family's nighttime routes. Ajax Night mode arms selected detectors according to the configuration.
If motion detection is excluded from an occupied area at night, decide which openings and glass remain monitored before finalizing the count.
Get a Sensor Plan for Your Home
Ask for an equipment list that identifies each detector's location, purpose, and arming behavior. Professional security system installation should include testing in final positions and an explanation of any remaining coverage gaps.
ASPEX Secure is an Ajax Systems Authorized Partner. We design, install, support, and offer professional monitoring for compatible home security systems in Houston.
Request a professional security assessment to plan sensor coverage around your home's doors, windows, layout, and daily routines.
