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Amazon sells roughly 355 different cat repellent products but judging by the consumer ratings, most of them don't actually work -- and even those that do, could be correlation rather than causation.

Do ultrasonic cat repellents work, or don't they?

There's already a question about ultrasonic insect repellents but it doesn't mention cats, so I'm opening this question specifically for (against!) cats and similar animals; as opposed to insects.

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The sub-sonic garden hose I have has been working quite well for me :) – Monkey Tuesday Aug 26 '11 at 21:52
Cats are very stubborn. You probably have to convince the cat before-hand so that the placebo effect (which is all you can probably hope for with cats) can make your investment in these products seem more worth-while. ;-D – Randolf Richardson Aug 27 '11 at 22:45
I use an ultrasonic bb gun. ;-> – Moab Aug 28 '11 at 2:28
I have found that they do repel ultrasonic cats very well. – user3344 Nov 15 '12 at 23:25
This site shows a secretly filmed video of cats being repelled by an ultrasonic device - and goes on to promote a product. But this site shows the WHOLE video - - and the WHOLE truth - that is,cats learn to ignore the deterrent. – user30410 Dec 23 '15 at 7:03
up vote 8 down vote accepted

Yes, they work... somewhat. They certainly affect behaviour, but it depends on the cat.

A "real-world" experiment showed some deterrence:

The efficacy of an ultrasonic cat deterrent, Sarah Helen Nelson, Andrew David Evans, and Richard Brian Bradbury, Applied Animal Behaviour Science Volume 96, Issues 1-2, January 2006, Pages 83-91

Ultrasound deterrents for a variety of mammals, including cats, are widely available in the commercial market, but few have been independently tested for efficacy. This study tested the efficacy of an ultrasonic cat deterrent ‘Catwatch©’, using 63 and 96 volunteer observers in two long-running (18 and 33 weeks) blind experiments. Results indicated that the device did have a moderate deterrent effect, reducing the probability of a cat intrusion into a garden by approximately 32% in the first experiment, but not in the second. The average duration of intrusions was reduced by approximately 38 and 22% in the two experiments, respectively. The magnitude of the deterrent effect appeared to increase with time, since the device was deployed. It is likely that the size of the deterrent effect could be increased by positioning the device(s) more carefully with regard to entry points to the garden that are regularly used by cats.

There has also been a study of cats in more "lab-like" conditions, that also showed differences in behaviour - but perhaps not the ones desired (emphasis mine):

Evaluation of the welfare implications and efficacy of an ultrasonic ‘deterrent’ for cats, D. S. Mills, S. L. Bailey, R. E. Thurstans, Veterinary Record 2000;147:678-680 doi:10.1136/vr.147.24.678

The effect of the ultrasonic output of a commercial cat ‘deterrent’ was assessed by measuring the behaviour responses of 10 cats in a standard test arena. The cats were introduced to the arena approximately nine metres outside the stated range of efficacy of the product and small food piles were placed at one metre intervals towards the device. When the cats were released from the basket, their behaviour and location were recorded continuously. The behaviour of the cats with the device on and off was compared by using a general linear model and chi-squared analysis. Differences between individual cats were a significant factor in explaining the variance associated with the amount of ‘relaxed behaviours’ (P<0.001), and the time spent within the range of the device (P=0.006). The only significant behaviour changes recorded when the device was on, were an increased likelihood of ear flicking (P<0.001), less time spent actively exploring (P=0.043), and an increase in the amount of time spent in the reported ultrasonic range of the device (P=0.003).

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Thank you! So the essence of your answer is that if it works at all, it's certainly not reliable - right? So if I'm interested in reliable cat repellant, ultrasonic is not the way to go. (Though I'm also not saying any other way works better.) – Torben Gundtofte-Bruun Aug 29 '11 at 6:34
If you are interested in reliable cat repellent, then no, ultra-sonic is not the way to go. Moving into speculation, I take heart from the line "Differences between individual cats were a significant factor." If your problem is one particular cat, and that cat happens to be susceptible, you may find it is reliable for that cat - i.e. it may work reliably on some cats, but it doesn't on all of them. Also note from the first study it may take a while (weeks?) to take full effect. – Oddthinking Aug 29 '11 at 7:38
For more reliable cat repellent, I suggest purchase of large dog. – Monkey Tuesday Aug 30 '11 at 3:56
@Monk, ah, I think I know how this turns out... – Oddthinking Aug 30 '11 at 4:13
I think the real problem here is the lack of a standard cat. Cats are very much individuals. – Loren Pechtel Apr 19 '15 at 21:59

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