How ultrasound works
Ultrasound is sound at a frequency that humans cannot normally hear. The human ear can normally hear frequencies from 20 – 20,000 Hz. However, the auditory nerve is most sensitive around 1000-4000 Hz. A conversation between two adults is typically 200-5000 Hz.
Humans sound perception and most other vertebrates – detect sound with their ears. Ultrasound, which emits frequencies above 20,000 Hz, cannot be heard by humans.
Ultrasound works in such a way that a frequency is emitted towards a certain hearing loss, which makes it uncomfortable for the animal to stay in the area. Every time the ultrasound frequency hits an obstacle such as a wall, sofa or similar, the frequency will be reflected and the effect will be reduced. In the same way that a large snowball loses size every time it hits an obstacle.
Most models with ultrasound to scare mice, rats, cats, dogs, birds etc. emit ultrasound into a room, which makes it uncomfortable for a given pest species to stay in the area. It should be noted that ultrasound cannot travel through walls or in rooms with a lot of furniture.
If you have pests in several rooms, you should basically have one ultrasonic scarer per room. room. This also applies, even if the manufacturer writes that the range is greater than the room. So despite the fact that an ultrasonic scarecrow has a coverage of, for example, 50 square meters, and your rooms are two small rooms of two by 20 square meters, the scarecrow will still only cover the one room where the scarecrow is set up. Therefore, you should buy a scarecrow for each room where rodents and other pests are not wanted in the home.
If you use an ultrasonic scarer, it can take 2-3 weeks before you get the full effect against mice and rats in your area. As rodents are creatures of habit, we recommend setting up traps to catch the mice and rats that already live/stay in the area. A scarecrow can then be set up to scare away new rodents in the area.
When setting up the scarecrow, you should basically, if possible, point the scarecrow in the direction you want the pest to follow (see illustrations at the top for best placement of scarecrows). If you have pests outdoors, it is important that you choose a model that is designed to be set up outside. Since not all models can withstand rain, cold and similar weather conditions.
On the vast majority of models, the power supply can be done with a battery or an adapter for insertion into the socket.
If you choose to use an adapter, you must remove the batteries, otherwise you may risk short-circuiting the device.
The picture at the top shows how you can advantageously set up scarers with ultrasound.
Frequencies and hearing for animals and humans
The table below shows the frequency of hearing for dogs, cats, rodents and many other animals.
Note that reporting the frequency range for hearing in dogs, cats and other species is not a simple task.
The table must therefore be regarded as indicative.
If you are reading this guide on a tablet, smartphone or similar - you should turn your screen to see the entire table.
Approx. Range (Hz)
Approx. Range (Hz)
Marten / Ferret
Chicken / Hens
Squirrel (Eastern Fox Squirrel)
Source for table: Louisiana State University