Pet-Friendly Alarm Systems: The Ajax Installer's Guide to Fewer False Alarms

If you fit intruder alarms in UK homes, pets are the single most common cause of the call-back you never get paid for. This guide is for installers specifying and commissioning pet-friendly alarm systems on the Ajax Jeweller range — what pet immunity actually means, where the published limits stop, how mounting height and sensitivity change the outcome, and which detector to pick for a cat that climbs, a Labrador that patrols, or a garden full of foxes. Every figure below is taken from Ajax's own published specifications and cited inline.

Pet-friendly alarm system guide for Ajax detectors — Pet immunity is a design decision, not a tick-box — detector choice, height and sensitivity all have to agree.

What this guide covers

The published limit: Ajax pet immunity is specified for animals up to 20 kg and below 50 cm in height, with correct installation at 2.4 m.
Height beats weight: a 4 kg cat on a worktop breaks immunity long before a 19 kg dog on the floor does.
Three sensitivity levels map to three animal sizes — and the default is not the pet-friendly one.
Detector picks per room: standard PIR, dual-technology, curtain, and photo-verifying detectors each solve a different pet problem.
Verification is the safety net: photo-on-alarm tells you it was the dog before anyone rolls a key-holder.

What makes an alarm system pet-friendly?

A pet-friendly alarm system is one whose detectors are chosen, positioned and configured so that a household animal moving normally does not generate an alarm, while a person moving through the same space still does. It is not a single product feature. On Ajax, three things have to line up: the detector's lens and processing, the mounting geometry, and the sensitivity setting in the app. Get one wrong and the other two will not rescue it — which is why so many "pet-immune" installs still nuisance-trip in week two.

The commercial argument matters too. Repeated false activations are what cost customers their police response and cost you unbilled visits. If the site is signalling to an ARC, read our guide to Ajax wireless alarm systems alongside this one — the detector decisions here are what keep the confirmation policy on your side.

How Ajax pet immunity actually works

Ajax detectors do not simply ignore small heat sources — they classify them. The PIR analyses the thermal diagram from the sensor, including infrared intensity, the size of the thermal spot and the character of its movement, and compares it against patterns typical of human motion. Ajax calls the algorithm SmartDetect, and it was built from thousands of recorded thermal patterns from humans, animals and environmental interference (Ajax MotionProtect product page).

Two practical consequences follow. First, an animal is rejected because its hotspot is small and low, not because it weighs little. Second, digital temperature compensation keeps the detector sensitive in warm rooms where ambient temperature approaches body temperature — the conservatory problem — so you are not trading pet immunity against summer blind spots.

The published limits: 20 kg, 50 cm, 2.4 m

Ajax specifies pet immunity for animals weighing up to 20 kg and below 50 cm in height, achieved with correct installation at a height of 2.4 m and the lens directed perpendicular to the likely intrusion path (Ajax). Treat all three numbers as one specification rather than three separate ones. Drop the detector to 2.0 m to hide it behind a bookcase and you have widened the part of the beam pattern that sits at animal height — the 50 cm figure no longer applies.

The Ajax MotionProtect U Jeweller (white) and its black counterpart detect motion up to 12 m across an 88.5° horizontal field, run up to seven years from a CR123A cell, and communicate up to 1,700 m in open space over Jeweller (Ajax). That is the workhorse for a normal pet household, provided you honour the mounting rule.

Three sensitivity levels — and which pet each one tolerates

Sensitivity is the setting installers most often leave alone, and it is the one that decides which animal the detector forgives. Ajax documents the three levels against animal height: high sensitivity does not react to cats up to 25 cm tall, medium does not react to small dogs up to 35 cm, and low does not react to animals up to 50 cm tall (Ajax MotionProtect manual). Medium is the factory default, so a household with a large dog needs a deliberate change at commissioning.

Sensitivity	Tolerates	Best for	Trade-off
High	Cats up to 25 cm	Cat-only homes, high-value rooms	Least forgiving of dogs and thermal drift
Medium (default)	Small dogs up to 35 cm	Terriers, spaniels, most cats	Not enough for a Labrador or a climbing cat
Low	Animals up to 50 cm	Large dogs at ground level	Slower to react to slow, distant human movement

Why height beats weight every time

The 20 kg figure gets quoted in sales copy; the 50 cm figure is what actually breaks installs. A 4 kg cat on a kitchen worktop, a stair landing or the back of a sofa presents a hotspot at roughly human trunk height, moving horizontally — which is precisely the pattern SmartDetect is built to alarm on. A 19 kg retriever padding across the floor stays in the rejected band all night.

So survey vertically, not just horizontally. Walk the room and ask where the animal can get to, not what it weighs: worktops, window sills, radiator covers, the top of the stairs, the arm of a sofa positioned in the beam. If the answer is "anywhere", stop specifying a wide-angle PIR for that room and move to a curtain or dual-technology detector.

Ajax detector choices for cat, dog and outdoor pet scenarios — Three reference builds: cat household, large-dog household, and a garden with wildlife traffic.

Dual-technology detectors for the difficult rooms

Where a PIR alone cannot separate the animal from the environment, add a second physics. The Ajax MotionProtect Plus U Jeweller (white) and black version pair the infrared sensor with a microwave sensor, so motion has to satisfy both before an alarm is raised. Ajax states the combination filters draughts, curtain and blind movement, light flicker, glare and reflections, keeps the same 20 kg / 50 cm pet immunity, detects to 12 m with three sensitivity levels, and runs up to five years from its internal battery over a 1,200 m Jeweller link (Ajax MotionProtect Plus).

That is the detector for rooms with a fireplace, an air-conditioning unit, a wood burner, or a large south-facing window — the same rooms where pets tend to sleep. If you are weighing the Ajax option against a wired-style alternative, our MotionProtect versus Pyronix KX comparison covers the trade-offs.

Curtain detectors: protect the route, ignore the room

A curtain detector solves the pet problem by geometry rather than by processing. The Ajax MotionProtect Curtain Jeweller throws a narrow vertical plane — 6° horizontal against 90° vertical — detecting to 15 m and running up to three years from its pre-installed battery (Ajax MotionProtect Curtain). Hang it beside a patio door or across a hallway and the animal can own the room; only something crossing the plane raises an alarm.

This is the cleanest answer for open-plan ground floors where the dog is left downstairs. Pair it with contacts on the perimeter — the Ajax DoorProtect U Jeweller on the doors and an Ajax GlassProtect U Jeweller on the glazing — and you get a genuine perimeter-first design that a pet cannot trigger from inside.

Motion plus glass break in one device

Where you want volumetric cover and glass-break detection from a single point, the Ajax CombiProtect (white) and black variant combine a PIR reaching 12 m across 88.5° with an electret microphone covering 180° and detecting breaking glass to 9 m using a DualTone verification algorithm. Pet immunity is the same 20 kg / 50 cm band, battery life is up to five years, and it is Grade 2 approved (Ajax CombiProtect).

Fitting one CombiProtect instead of a PIR plus a separate glass-break sensor also reduces the number of devices a pet can walk under, which is a quiet but real benefit on a small hub budget.

Photo verification: proof it was the dog

Pet immunity reduces false alarms; verification removes the argument about the ones that remain. The Ajax MotionCam U Jeweller takes a series of photographs when it alarms, and the MotionCam U (PhOD) variant adds photos on demand. Ajax documents three photo resolutions — 640×480, 320×240 and 160×120 — and the same three sensitivity levels mapped to 25 cm, 35 cm and 50 cm animals, with detection to 12 m across 88.5° and up to four years from two pre-installed CR123A cells (Ajax MotionCam manual).

For a monitored site with animals, a photo-verifying detector in the highest-risk room is the cheapest insurance you can specify. It also gives you a diagnostic tool: if the customer reports nuisance activations, the images tell you within a day whether you are looking at a cat on a worktop or a genuine sensitivity problem.

Outdoors: foxes, cats and the neighbour's dog

Garden detection is where pet-tolerance design gets hardest, because you cannot control what walks through. The Ajax MotionProtect Outdoor and the photo-verifying Ajax MotionCam Outdoor use paired sensors and masking logic to hold down wildlife activations. For a driveway or boundary line, the narrow-plane approach wins again: the Ajax Curtain Outdoor Jeweller and the bidirectional Ajax DualCurtain Outdoor watch a line rather than an area, so a fox crossing the lawn behind the plane is simply not in the detection zone.

Our security fog systems guide covers what happens after an outdoor detection is confirmed, if the site justifies an active response.

Non-pet false alarms you still have to design out

Blaming the cat is convenient, but a lot of "pet" activations are nothing of the sort. Work through the same checklist on every survey: heating pipes and radiators inside the beam, a boiler flue on an external wall, sunlight tracking across a floor in the afternoon, a tumble dryer vent, helium balloons after a birthday, and curtains over a draughty sash window. Dual-technology detectors handle most of these; repositioning handles the rest.

Radio coverage is the other silent cause of call-backs. Ajax detectors report signal quality in the app, and where a garage or outbuilding sits at the edge of range, an Ajax ReX 2 Jeweller range extender keeps photo-verifying detectors connected rather than dropping to intermittent contact.

Six-step commissioning workflow for a pet-friendly Ajax alarm system — Survey, mount, set sensitivity, walk-test with the animal present, verify, then hand over.

A worked example: three-bed house, two dogs and a cat

A typical Leicester semi with a Labrador, a spaniel and an indoor cat that uses the worktops. The hub is an Ajax Hub 2 (2G) where Ethernet plus a single cellular path is enough, or an Ajax Hub 2 Plus where you want Wi-Fi and dual SIM as well.

Area	Pet problem	Detector	Setting
Kitchen / diner	Cat on worktops overnight	MotionProtect Curtain across the back door	Plane clears the worktop line
Hallway	Dogs sleep and patrol	MotionProtect U at 2.4 m	Low sensitivity
Lounge (bay window, log burner)	Thermal interference plus dogs	MotionProtect Plus U	Low sensitivity, microwave active
Landing	Cat climbs the stairs	MotionCam U (PhOD)	Medium, photo verification on
Rear garden	Foxes and neighbouring cats	DualCurtain Outdoor on the boundary	Plane along the fence line

Arming is where pet households trip themselves up, so specify the arming device with the same care: our Ajax keypad comparison covers night-mode and partial-arm behaviour, which is what lets a customer keep the dog downstairs without disabling the whole ground floor.

Common mistakes that break pet immunity

Five recurring errors account for most of the pet-related call-backs we hear about from installers:

Mounting low to hide the detector. Below 2.4 m, the published immunity no longer holds.
Leaving sensitivity on medium in a large-dog household, when low is the specified level for animals up to 50 cm.
Aiming down a corridor the pet uses instead of perpendicular to the intrusion path.
Ignoring furniture the animal can climb — a sofa back or worktop inside the beam is a hotspot at human height.
Walk-testing without the pet. Test with the animal loose in the room, at night, before you leave site.

Where a property already has wired detectors you want to keep, the Ajax MultiTransmitter brings them onto the same hub, so pet-zone logic can be applied consistently across old and new devices.

Frequently asked questions

Is Ajax pet immunity guaranteed?

No manufacturer guarantees zero activations. Ajax specifies immunity for animals up to 20 kg and below 50 cm in height with correct installation at 2.4 m; outside those parameters the behaviour is not specified. Design to the published limits and verify on site.

Which Ajax detector is best for a large dog?

A MotionProtect U or MotionProtect Plus U at 2.4 m on low sensitivity, which Ajax documents as the setting that does not react to animals up to 50 cm tall. Add a curtain detector where the dog has run of an open-plan space.

Why does my customer's cat set off a pet-immune detector?

Almost always because the cat gets above 50 cm — worktops, sofa backs, stair landings, window sills. Re-aim the detector, raise the beam clear of the climbing surface, or switch that room to a curtain detector.

Does pet immunity reduce detection of a person?

Lower sensitivity makes the detector less reactive overall, so a slow, distant human movement is detected a little later. On a correctly aimed detector at 2.4 m this is not a practical loss for domestic room sizes, but it is a reason not to run low sensitivity in every zone by default.

Do I need photo verification on every detector?

No. Put photo verification where the value or the false-alarm risk is highest — usually the main circulation route and any room where the pet has access. One MotionCam in the right place resolves disputes faster than four in the wrong ones.

Can outdoor detectors ignore foxes and cats?

Partly. Outdoor PIRs use paired sensors and masking logic to suppress small animals, but the more reliable approach outdoors is geometry: a curtain or bidirectional detector watching a line, so wildlife crossing elsewhere in the garden is never in the detection zone.

Related guides

Order Ajax pet-friendly detectors from Netview

Netview is an authorised UK Ajax stockist based in Leicester. The detectors in this guide are held in stock for same-day dispatch, with trade pricing for installers. Browse the full Ajax range and order online at netviewcctv.co.uk.

August 14, 2026 | View: 1 | By: netviewcctv.co.uk

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