Independent comparisons. We may earn from shop links. More info

PIR sensor false alarms: aim and heat before you replace it

Updated: 20.10.2026

PIR sensor false alarms usually mean the lens is doing its job on the wrong patch of heat. The lamp or the chime has fired, and nobody is obvious in the frame. Before you replace anything from the [motion sensor comparison](/hub/burglar-protection/motion-sensor), re-aim the head and set the light threshold. A failed sensor is the later conclusion, after plants, traffic, animals, and rain are ruled out. Nothing in this amazon.co.uk set, checked on 19 October 2026, states a pet-immune distance. If the mains head is not isolated yet, the limits are on [how to install a PIR sensor](/hub/burglar-protection/motion-sensor/sub/motion-sensor-how-to-install).

PIR sensor false alarms usually mean the lens is doing its job on the wrong patch of heat. The lamp or the chime has fired, and nobody is obvious in the frame.

Our top picks

Maclean Maclean MCE468 B

Best overall

Maclean Maclean MCE468 B
9.2/10about £10.96
View offer
SEBSON SEBSON IR_OUT_AA

Alternative

SEBSON SEBSON IR_OUT_AA
8.6/10about £13.99
View offer
BeiLan BeiLan PIR chime

Alternative

BeiLan BeiLan PIR chime
8.6/10about £15.89
View offer
On this page
  1. 1.It sees moving heat, not people
  2. 2.Plants, traffic, puddles, and rain
  3. 3.Cats and foxes
  4. 4.On all day, or too keen a chime

It sees moving heat, not people

A PIR compares infrared across a segmented lens. A person, a warm car, a cat, or a branch in front of a sun-heated wall can all look alike. Wind alone is a weak explanation. On a Maclean or outdoor SEBSON, tilt the 180° field off the pavement. A 12 m head on a front corner can see the footpath. Turned toward the door and down to the step, it often goes quiet. Masking tape on the unwanted edge of the lens is a fair test.

Plants, traffic, puddles, and rain

DCC Electrics names vegetation, traffic, pets, reflections, and rain that shortens range. Voltimum adds a sun-warmed wall behind moving plants. Cars count as a detection if the pattern reaches the road. Rain on the lens can false-trigger, which is not water inside a seal. Outdoor SEBSON units are IP44; leaks on an open wall are a rating problem on the motion sensor buying guide. The Maclean is IP65. If the terminals are wet, stop using the head.
Maclean Maclean MCE468 B

Testsieger

Maclean Maclean MCE468 B
9.2/10about £10.96
View offer

Cats and foxes

Which? found that 21 per cent of surveyed alarm owners blamed a pet and 9 per cent an animal outside. That is not a test of these listings, and no kilogram limit is printed. One Maclean garden review and one BeiLan cat-doorbell review are not a pet-immune specification. The indoor SEBSON IR_ES_A, 6 m at 360° and IP20, will see a dog under it.

On all day, or too keen a chime

A lamp on all afternoon is often the lux dial, about 3 to 2,000 on SEBSON and Maclean. Turn it toward the low end so the sensor arms after dusk. Hue uses a daylight sensor in the app. Tapo prints no lux figure, so day and night are a schedule. BeiLan can gap alerts by 15 or 30 seconds only. Move it off the pavement or drop the volume within 25–80 dB. If you replace it on purpose, use best motion sensor.

Common questions

Can wind itself trigger a PIR?
Wind alone is a weak explanation. What installers describe is something moving in front of a surface the sun has warmed. A shrub against a brick wall on a bright day is the usual case. Cut that branch out of the field, or turn the head, before you call the detector faulty. Rain on the lens is a separate cause and can false-trigger even when the bushes are still.
Will it ignore my cat?
Not on any listing in this set. No Maclean, SEBSON, Hue, Tapo, SONOFF, Eve, or BeiLan page states a pet-immune weight. Which?’s survey figure is about alarm owners, not these products. You can aim above a cat’s usual path and still catch a fox on a bin. One BeiLan owner uses the chime as a cat alert, which shows the lens sees the animal.
Why is it on all day?
The threshold is probably set for daylight. On SEBSON and Maclean heads, move lux toward a few lux so the switch is armed only after dark. Hue uses its daylight sensor in the app. Tapo has no illuminance control on the listing, so you need a schedule. A lamp that stays on at noon with the dial already at the moon end is a different fault. Check that with the power isolated, not by guessing at a live terminal.
Do cars on the road count as a fault?
They count as a detection if the pattern reaches the road. A 180° head at 12 m on a front corner often includes the carriageway. SEBSON reviewers describe constant triggering when the head faces the pavement. Swing it toward the door and tilt it down. The car can stay visible to you and invisible to the PIR. That is an aiming job, not a reason to replace the sensor.
Should I replace it if it false-triggers in heavy rain?
Not on the first wet night. Rain on the lens can false-trigger, and heavy rain can shorten range. Dry the lens, confirm the interior is not wet, and test again in clear weather. Water inside an IP44 SEBSON that was mounted in the open is a rating problem. An IP65 Maclean with a dry box and a wide aim is still an aiming job. Replace it when the same fault remains on a dry night after the head has been narrowed.
The chime is too keen. Is that the same fault?
It is still a PIR looking at too much heat. The BeiLan kit can only gap alerts by 15 or 30 seconds, and reviews say it is over-sensitive, with no fine trim beyond placement. Site it off the pavement, use the 30-second gap, and lower the volume. It has no lux dial to cure a daytime chatter. If it is wet inside, the title’s weatherproof line was never an IP rating.

Related pages

PIR versus smart sensors

Motion sensor

Best motion sensor UK: one top pick, and who skips

Motion sensor buying guide: choose lamp, hub, or chime

How to install a PIR sensor on an existing UK cable

Sources

Public UK sources and the amazon.co.uk listings kept on 19 October 2026.

  1. Electrical Safety First, outdoor lighting (retrieved 19.10.2026)
  2. Approved Document P (GOV.UK PDF) (retrieved 19.10.2026)
  3. legislation.gov.uk, SI 2012/3119 regulation 6 (retrieved 19.10.2026)
  4. GOV.UK, when approval is not needed (retrieved 19.10.2026)
  5. KES Lighting, IP65 vs IP44 (retrieved 19.10.2026)
  6. Professional Electrician / Ovia, PIR and microwave sensors (retrieved 19.10.2026)
  7. DCC Electrics, PIR security lighting (retrieved 19.10.2026)
  8. Voltimum UK, motion-sensor interference (retrieved 19.10.2026)