Do Cat and Dog Repellers Actually Work? An Honest Assessment
We manufacture these devices. We're still not going to promise you a guaranteed result, because in this category nothing destroys trust faster than a promise that can't be kept.
How ultrasonic deterrents work
The device emits high-frequency sound above the human hearing threshold. Most adult hearing tops out around 17 kHz; cats and dogs hear well beyond it. That gap is the entire operating principle: a space that stays silent for you becomes unpleasant for the animal.
Most garden units include a PIR motion sensor, which reads the thermal silhouette of a warm body moving against a cooler background and fires only when something crosses its arc. That does two useful things — it extends battery life, and it means the unit isn't running pointlessly all day.
The important part: the device never touches the animal and causes no lasting harm. All it does is persuade the animal to drop that corner from its daily round.
Why cats respond more reliably
Cats are creatures of routine. Once a patch of lawn, a flower bed or a vegetable border enters a cat's mental map, it returns almost daily, often at the same times.
It's using your garden for three things: territory marking, toileting and hunting. The first is the most stubborn, because the scent of urine draws both the same cat and its rivals back, layer after layer. Do nothing and the problem gets worse rather than better.
This is exactly where a deterrent earns its place. Instead of chasing the cat off with a shout from a window — which teaches it only to avoid you — the unit interrupts the visit silently, from a fixed point, every single time. The cat can't tell where the sound comes from. It only learns that this corner is now unpleasant, and its instinct is to stop coming.
The reason success rates are high with cats is simple: the cat isn't dependent on your garden, it has alternatives, and the cost of the disturbance is high relative to the reward.
Placement rules for cats
- Aim the sensor at the entry point. Cats don't fall out of the sky — they use known routes: the top of a fence, a gap under a gate, a specific bed. Point the unit at the route, not at the middle of the garden.
- Mount it 20–30 cm off the ground. Too low and the PIR is confused by grass movement; too high and it watches empty air above the cat.
- Don't point it at heat sources. Sun-warmed brick and tumble-dryer vents cause false triggers.
- Keep the sensor lens dry. Even a weather-rated unit "sees" poorly through direct rain on the lens. A small overhang helps in exposed spots.
- Clean existing scent marks. In the first week, treat marked spots with an enzyme-based cleaner. This removes the "this is mine" signal that keeps drawing them back, and it makes the device's job considerably easier.
Why dogs are less predictable
Results with dogs vary far more, and there's an honest explanation for it.
Owned dogs, habituated to people, respond less. These animals are already adapted to human proximity and household noise; an unpleasant sound often isn't enough to make them give up a space.
Wary dogs that keep their distance from people respond more. For them the space is a preference rather than a habit, and when the cost rises they reroute.
Every dog has a different hearing range and stress threshold. The same unit producing two different outcomes in two dogs isn't a fault — it's expected. Older dogs also lose high-frequency hearing, exactly as people do.
The practical conclusion: treat a dog deterrent as one layer working alongside physical barriers and food-source control, not as a standalone solution.
Habituation: the real enemy
The nervous system filters out a stimulus that repeats identically and predictably without consequence. It's why you stop hearing your own refrigerator a day after moving in.
For the same reason, a device holding one fixed tone becomes background noise within weeks. That mechanism is precisely what sits behind the common "it worked for a week and then stopped" review.
The answer is a frequency that doesn't stay still. A unit that sweeps continuously and unpredictably across a band gives the nervous system no stable pattern to file away.
When you read a spec sheet, this is the line that matters: a frequency range and the word sweep — not a single number. A product that won't state its range probably doesn't sweep.
How long it takes
Visits often drop noticeably. The habit isn't broken yet.
In most gardens, this is where the habit breaks.
Territorial animals, or gardens shared by several cats, can take this long for a full result.
Review the unit's aim after the first week — a side approach you didn't spot initially is the most common thing that turns up.
If a dog approaches you aggressively
This section has nothing to do with any product, and getting it right matters. The guidance below follows veterinary and animal-welfare organisations.
Do not run. However strong the instinct, running triggers the chase response. If a dog is running at you, stay where you are.
Stand side-on. Turning your side to the dog rather than facing it square makes you look less threatening.
Avoid direct eye contact. A direct stare reads as a challenge. Look down or away while keeping the dog in your peripheral vision.
Do not shout. This is common advice and it is wrong. A sudden loud noise raises the dog's arousal rather than calming it. Staying quiet and still is safer.
Keep your arms still. Moving limbs increase the risk of a bite. Hold your hands close to your body.
Put a barrier between you. A bag, a coat, an umbrella, a bicycle, a car door, a tree — anything. If you're cycling, dismount and keep the bike between you and the dog as you move away slowly.
Don't hit the dog. Physical retaliation usually escalates aggression.
If you're knocked down, curl up. Pull your knees to your chest and cover the back of your neck and ears with your hands. Use a bag or coat as a barrier between the dog and your head and neck. Stay still.
Get medical attention for any bite. Even superficial wounds carry infection and, depending on the country, rabies risk. Don't wait to see how it develops.
An important distinction
The advice for wild boar is partly the opposite — there, making noise from a distance and getting to higher ground is correct. Don't apply the same reflex to both animals. See our wild boar guide.
One device, or layered protection?
No deterrent outcompetes an open food source or an unsealed entry route.
Three layers together give the best result:
- Remove the food. No pet bowls left outside, bins closed and secured, fallen fruit collected.
- Build the physical barrier. Gaps at the base of fences, gate thresholds, favourite crossing points — make the animal's route harder.
- Place the device correctly — right point, right height, running continuously.
The three together do noticeably more than any one of them alone.