Ultrasonic pest repellers do not reliably work, and where they have any effect at all it is partial and short lived. The plug-in units sold for mice and rats may make the animals wary for a few days, but rodents quickly learn that the sound carries no real threat, and the devices do nothing about the food, warmth and way in that brought them indoors in the first place. The UK's advertising regulator has examined the evidence for these products and has yet to accept a single claim that they work.
The people who buy them are usually doing something sensible, looking for a quiet, poison free answer to scratching in the walls. The problem is that ultrasound is a poor tool for the job. It travels a short distance, it will not pass through walls or floors, and furniture blocks it completely, while mice and rats spend most of their time inside exactly the spaces it cannot reach. If you have a repeller plugged in and are still hearing noises or finding droppings, the device is not about to start working.
What the evidence says
The clearest verdict comes from the Advertising Standards Authority, which regulates advertising claims in the UK. It has examined the evidence behind pest repellents ranging from ultrasonic and electromagnetic units to novelty deterrents, and says it has yet to accept any claim of efficacy. Its guidance to advertisers is that without evidence from UK based trials they should not state or imply that a repeller works, and that customer testimonials do not count as evidence on their own.
The scientific research points the same way, and it is not new. Researchers at the US Denver Wildlife Research Center, reviewing earlier work while designing test protocols for ultrasonic rodent repellers, noted that commercial devices had been shown to produce only partial and temporary repellency in wild rats, and that manufacturers had begun selling them on the back of sparse and inconclusive data. The regulator's guidance, written decades later, reaches the same conclusion.
Why mice and rats get used to the noise
Rodents are cautious about anything new in their surroundings, which is why a repeller can appear to work for the first few nights. A new sound in a familiar place is enough to make a mouse hesitate. But caution only lasts while there is a reason for it. When the noise is constant and nothing bad follows, the animals stop reacting to it, and once there is food on the other side of the sound, the hesitation disappears quickly.
Why the sound cannot reach where they live
Ultrasound behaves more like light than like ordinary noise. It travels in straight lines, it is absorbed by soft furnishings, it bounces off hard surfaces, and it leaves a shadow behind every sofa, cupboard and kitchen unit. A unit plugged into a kitchen socket covers part of the open floor of that one room and nothing else.
Mice and rats, meanwhile, live in the places a socket cannot see. They travel inside cavity walls, behind kickboards, under suspended floors and through the loft. Mice commonly get in through gaps around pipework, damaged air bricks, the loft and small openings beneath kitchen units. Many of the older terraces in Folkestone and Hythe have suspended timber floors over voids that run the length of the row, so mice can travel from house to house underneath the floorboards and surface anywhere. A repeller in one kitchen has no effect on a mouse running through a void beneath it. The same applies behind the weatherboarded and tile hung walls common across the area, where a continuous cavity sits behind the cladding.
Proofing with materials a rodent cannot gnaw through lasts where a temporary DIY fix often does not, because mice and rats can chew through many common materials. One customer's Google review describes a job like this. Field mice were coming in through the air bricks, so John trapped them and sealed every entry point, and there have been no problems since. A mouse that cannot get in does not need scaring away, while a mouse that can get in soon learns to ignore the noise. Proofing deals with the cause. A repeller, at best, deals with a symptom for a few nights.
Why autumn is when people reach for them
Autumn is when most people first hear mice in the house, and the timing is no accident. On the farmland edge around Ashford, Canterbury and the Weald villages, harvest and ploughing strip cover and food out of the fields at the same time, and mice and rats move towards buildings. Across Romney Marsh, the network of dykes and watercourses gives rats a ready made route to outbuildings and then houses. Calls about rodents climb from autumn for those reasons, and the first scratching in the loft or behind the cooker is often when a repeller goes into the basket.
That is also the worst time to rely on one, because a mouse that gets into the house in October has the whole winter to breed somewhere warm.
What about other pests
The same limits apply beyond rodents. Ultrasonic devices sold for gulls have no reliable effect either, which is one reason that keeping seagulls away comes down to physically denying them a place to land and nest. Units marketed for insects, spiders or cockroaches face the same problem with the evidence, and the regulator's position covers them all. If a product claims to repel everything from mice to ants with one plug, that breadth of claim should make you more sceptical, not less.
What works instead
Effective rodent control starts with finding out how the animals are getting in and why they are staying. That means a survey of the outside of the building and the voids inside it, identifying the species, finding the runs and harbourage, and then closing the entry points with materials a rodent cannot gnaw through.
- Proofing the gaps around pipes, cables, air bricks, doors and kickboards, with stainless steel mesh and fixings on exposed coastal elevations, where salt laden wind corrodes ordinary galvanised steel within a few winters.
- Removing food and shelter, with sealed food storage, secure bins and less clutter in lofts, sheds and garages.
- Targeted treatment with traps and baits placed by a trained technician in the runs where they will be taken, rather than in the middle of the floor.
Proofing is the part that decides whether the problem stays solved, and it is why our rodent treatment combines traps and baits with pest proofing. It is also the honest answer to whether pest control can stop mice coming back. Treatment clears the mice that are there, and proofing stops the next ones following them in. Our rodent control service covers both.
If your repeller has not worked
If you have a repeller plugged in and you are still finding droppings or hearing movement at night, the honest advice is to unplug it and look at how the mice are getting in. The sooner the entry points are found and closed, the fewer mice there are to deal with.
At Cinque Ports Pest Control we are a family run business based in Dymchurch, with more than twenty-five years in the trade behind us, and we deal with mice and rats in family homes, rental properties, lofts, restaurants and commercial units across Romney Marsh, Ashford, Canterbury, New Romney, Lydd, Folkestone and Hythe. If you are hearing something in the walls, get in touch and we will find out how it is getting in.
Cinque Ports Pest Control Ltd is a family run business based in Dymchurch, Romney Marsh. We are BPCA members, Kent County Council Trading Standards approved, TrustMark registered, SafeContractor approved and CRRU supporters.
