Configuring motion sensors so pets stop setting off alarms is mostly practical work and a few smart choices. I walk through the parts that matter, from picking the right hardware to making small physical changes that cut cat detection. I use smart home conventions and Home Assistant examples because that’s what I run and what most hobbyists use. Read this, do the tests, change one thing at a time and record what happens.
Start with the sensor. Passive infrared, PIR, is the common choice. PIR spots heat and motion. Some PIR models are sold as pet‑immune or have an adjustable pet setting. Dual‑technology units pair PIR with microwave or ultrasonic sensing and can reduce false positives, but they can be fussier to tune. Check the datasheet for “pet immunity” or adjustable sensitivity before you buy. Mounting matters more than most people expect. Aim to mount at about head height, around 2.0–2.3 metres, angled slightly down. That keeps the main detection cone away from a cat’s normal roaming band. Avoid pointing a sensor straight at a floor area where pets run, at vents, at heating sources or at reflective surfaces that throw heat signatures around. Set sensitivity to medium at first. Run a walk test and a pet test. For the walk test stand where the motion sensor should trigger and move through its field. For the pet test get the cat to move through the lower half of the detection cone while you watch the sensor or Home Assistant binary sensor state. If it triggers too easily, drop sensitivity in small steps and test again. Common problems include low mounting, windows in the detection field, and drafty vents. Fix those first before messing with advanced settings.
If you still get false alarms, try low‑impact physical fixes next. One simple trick reported by users is painting the lower half of the monitored wall. The idea is to change the surface the sensor “sees” in the lower part of its cone. Paint can absorb or disperse the heat/contrast signature enough to prevent small animals from showing up as full motion. Do this in stages:
1) Paint the lower 60–100 cm of the wall with a matt emulsion.
2) Test detection for 24–48 hours.
3) If false triggers continue, apply a second coat and test again.
Users on Home Assistant forums said one coat sometimes reduced triggers, two coats stopped them. Keep the painted band horizontal and even, not patchy. Where painting is impractical use a physical barrier or baffle: a low transparent panel or a strip of textured fabric fixed to the wall can achieve the same effect. You can also fit a small cone or collar around the sensor to narrow the field of view. Those little sensor hoods are cheap and reversible.
Tune the automation logic, not only the hardware. In Home Assistant use conditional logic to ignore short, low‑priority motion events. For example, require the sensor to be active for 30 seconds before logging an alarm or trigger a notification only when nobody is home. A pragmatic rule set I run: motion must be present for at least 20–30 seconds, then check that an authorised person is not present, and only then trigger an alarm. Make the change, then validate by watching the binary_sensor state and by letting the pet move in the area for a day. If automatic camera snapshots are set, check them to confirm the event was real before escalating to alarms. If a sensor offers adjustable retrigger time, increase that slightly to avoid repeated events from the same pet crossing back and forth.
Keep a maintenance routine. Check batteries monthly for battery‑powered sensors and dust or insect screens for wired ones. Re‑test after any furniture move or seasonal change like heating coming on, because thermal patterns change. Log each tweak and its result. A short table in your notes with columns: change made, date, test length, result, gives a fast way to roll back a tweak that makes things worse. Concrete takeaways: choose a sensor with pet options, mount it higher and angle it down, test with the actual pet, change one variable at a time, and try a painted lower band or a small physical baffle before buying more kit. That method gets motion sensors behaving without turning the house into a nuisance alarm.
