Ajax MotionProtect (Standard and Plus): What It Detects and How to Run It

The Ajax MotionProtect is a battery-powered indoor movement detector for an Ajax burglar alarm. It watches a room for the heat signature of a moving person and tells the hub when it sees one, so the alarm can sound. The standard version covers a zone 12 m wide with an 88.5° view, and Ajax gives a calculated battery life of up to 5 years from one CR123A cell, with the hub checking in every 3 minutes¹.

If you are choosing between the two versions, the difference is the extra sensor. MotionProtect Plus adds a microwave sensor alongside the usual passive infrared (PIR) element, which makes it harder to fool, and Ajax states it does not react to animals up to 50 cm tall¹. Both are for indoor use only, both ignore movement behind glass, and both are set up and tested from the Ajax app.

This page covers what each version does, where to mount it so it actually sees the room, how to change the battery safely and how to keep it working. For the wider question of what kind of alarm suits a household, start with Burglar Alarms: Types and How to Choose One.

What the MotionProtect does, and which version to fit

A PIR detector works by sensing changes in heat, or infrared energy, within a room, and triggers the alarm if the system is armed⁴. Every person, pet and warm object gives off that heat, so a moving person crossing the detector's view produces the change it is looking for. The MotionProtect is Ajax's indoor version of that idea: a wireless unit that talks to an Ajax hub over the Jeweller radio protocol and runs on its own battery, so there is no wiring to run to the corner of a room³.

The two versions differ in how they confirm a detection:

The Plus is the one to consider where a single PIR might be triggered by something other than an intruder, because the second sensor has to agree before an alarm is raised. The standard version is the simpler choice for an ordinary room. Both use temperature compensation, which Ajax says is used in all its motion detectors so that the device recognises motion across its whole operating temperature range¹.

Neither version contains a camera. A PIR detector senses heat rather than taking pictures⁴. If you want images with the alarm, that is a different product: see Ajax MotionCam.

Detection range: a 12 m zone with an 88.5° view

The standard MotionProtect monitors an area within a 13 m radius, with a horizontal viewing angle of 88.5° and a vertical viewing angle of 80°³. Ajax gives the width of the detection zone as 12 m, and the detector is intended to be installed at 2.4 m without obstruction to its view³. The MotionProtect U datasheet gives the same 88.5° horizontal angle and a detection distance of up to 12 m when installed at a height of 2.4 m².

Those figures describe a cone, not a circle. The detector sees furthest straight ahead and less to the sides, and there is a blind zone close to the unit: Ajax lists 2.3 m for the standard model³. In practice that means a detector in the corner of a room covers the floor and the far walls well, but a person who comes right up under it may be missed. It also means the quoted range assumes the mounting height Ajax specifies; fit it lower or higher and the shape of the zone changes.

The detector responds to movement at speeds from 0.3 to 2 m/s, and sends an alarm no more than once every 5 seconds³. Someone walking normally falls inside that band. Very slow movement, such as a crawl, may not register.

Where to mount it, and where it will not detect

Mount the detector in the corner of the room or on a flat, firm vertical surface, at 2.4 m, with a clear view across the space³. Ajax warns that an unstable surface can lead to false alarms, so avoid a shelf that flexes or a wall that vibrates³. The intended path of an intruder should run perpendicular to the axis of the detector's lens, so that they cross the zone rather than walking straight towards or away from it³.

Keep it at least 1 m from the hub or a radio signal range extender, because closer than that can cause a loss of communication³. Double-sided tape is for temporary installation only: Ajax notes that while the device is taped, the tamper will not be triggered when it is detached from the surface, so a taped detector is not protected against being pulled off³.

Where it will not detect:

• Behind glass. Ajax states plainly that MotionProtect does not register motion behind glass, and the same applies to the Plus¹. A glazed door, a window or a glass partition is a blind spot.
• Below its temperature range. Effective motion detection runs from −10 °C to +40 °C on the standard model². Ajax lists a detector temperature outside those limits as a malfunction condition³.
• Very close underneath it, inside the 2.3 m blind zone³.
• When something is blocking the lens. The Plus has anti-masking, and Ajax says it is always active and operates regardless of the detector or system security mode⁵.

If you are placing several detectors, Ajax advises at least 20 cm between a MotionProtect Plus and another MotionProtect Plus, a Superior MotionProtect Plus or a Superior MotionProtect Plus Fibra¹.

Battery: up to 5 years on one CR123A

The standard MotionProtect takes one CR123A battery at 3 V, and Ajax gives a calculated battery life of up to 5 years from the pre-installed cell, with the hub checking in every 3 minutes³. The Plus carries the same up to 5 years figure under the same 3 minute inquiry frequency¹. The MotionProtect U datasheet also states a calculated battery life of up to 5 years².

That figure is a calculation, not a promise. Ajax notes that if other batteries are installed, the operating time may differ from the calculated time⁶. For the standard model Ajax recommends specific cells to ensure the device operates for the calculated time: a Panasonic CR123A Industrial lithium battery at 3 V, or a Huiderui CR123A at 3 V, 1,600 mAh, LiMn02⁶. The battery status in the app does not update instantly but within a ping period, by default every 36 seconds⁶.

When the battery runs low, you are not left without warning. Ajax says that after sending a low battery notification the detector can work for up to 2 months, which is your window to change it³. The low battery threshold on the MotionProtect U is 2.5 V². On the outdoor model a slow green flash during an alarm means the batteries need replacing but the detector carries on working; that indicator is described for the outdoor unit, so check the app for the indoor one⁵.

Changing the battery safely

Ajax's own procedure for the MotionProtect is to remove the detector from the SmartBracket mounting panel, switch the device off, loosen three screws and remove the front back of the detector, change the battery observing the polarity, reattach the back panel and tighten the three screws, then turn the detector on and check the battery status in the mobile application⁶. Use a new CR123A of the type Ajax specifies⁶.

That instruction matters more than it looks. The government's battery safety guidance warns that damaged batteries can catch fire rapidly and without warning, and advises checking your battery regularly for signs of damage and replacing it if you suspect any, without charging or using it⁷. A CR123A is not a rechargeable cell, so never attempt to charge one.

A few practical points. Work with the system disarmed so you do not set off the alarm while the casing is open. Keep the screws somewhere safe, because the back panel has to go back on and be tightened before the detector will sit properly on its bracket. If you have a Plus, remember that anti-masking is always active, so covering the lens during the change may itself produce a signal⁵.

Connecting to a hub, signal and testing

A MotionProtect works with one hub at a time. When you connect it to a new hub, it stops sending events to the old one¹. Ajax notes for the outdoor model that the device is not removed from the old hub's device list automatically, so tidy that up in the app yourself⁵. Devices are added to an Ajax hub by scanning their QR codes through the Ajax apps⁹. If a connection attempt fails, Ajax advises turning the detector off and trying again in 5 seconds³.

Signal strength is shown in the app as bars. Ajax recommends 2 or 3 bars, and states that repositioning even by 20 cm can significantly improve the signal strength¹. With one bar or none, stable operation is not guaranteed³. This is the single most useful adjustment on a detector that keeps dropping out, and it costs nothing but a few minutes with a screwdriver.

Entry and exit delays are set in the app and run from 5 to 120 seconds, including in Night mode¹. Set the exit delay long enough to leave and lock up, and the entry delay long enough to reach the keypad and disarm.

To test the zone, use the detection zone test in the app and walk across the protected area. Ajax's pass mark is 5 reactions out of 5; if the detector does not react in 5 out of 5 cases, relocate the device or change its sensitivity¹. The standard model has three sensitivity levels, and the setting changes how it treats pets: high ignores cats up to 25 cm tall, medium ignores small dogs up to 35 cm tall, and low ignores animals up to 50 cm tall³. Medium is the default³.

Upkeep, service life and warranty

Ajax gives the standard MotionProtect a service life of 10 years and a warranty of 2 years after purchase, which does not apply to the pre-installed battery³. The MotionProtect U datasheet lists a 24 month warranty². The Plus carries the same 2 year warranty on the same terms¹.

For routine upkeep, Ajax advises checking the detector once every three months³. That check is simple: run the zone test, look at the signal bars, confirm the battery status in the app and wipe the casing. Cleaning is where people do damage. Ajax states that you must not use any substances containing alcohol, acetone, petrol or other active solvents for cleaning the detector¹. Use a soft dry cloth, and wipe the lens carefully, because scratches can reduce sensitivity⁵.

The detector also reports on itself. It raises a tamper notification on attempts to detach it from the surface or remove it from the mounting panel². If the temperature reading in the app looks wrong, Ajax allows an acceptable error of 2 °C between the app value and the room temperature³.

If something is wrong that the app cannot explain, Ajax's technical support is reached at support@ajax.systems, with an AI-powered chatbot and a professional technical support team available 24/7⁵. For how this detector fits into a wider system, see Ajax Hub (2 Plus, 2, Plus) and Monitored or Self-Monitored Alarm?.