An ultrasonic Cat repeller creates an uncomfortable environment that a cat wants to get away from. Most have an PIR motion detector, that when a cat moves infront of it, activates the ultrasonic noise that most cats hate. It’s not painful or cruel, just annoying to a cat.
The most common reason for purchasing such a device is to stop cats fouling on your lawn or flower bed. If you aim the ultrasonic repeller in the general direction of where the cat is pooing, it should work fine.
There are a few points to mention about positioning the ultrasonic cat repeller. They don’t work through bushes, shrubs, hedges or anything else that is an obstacle. The unit needs a clear line-of-sight for both the PIR motion sensor to be able to detect movement and the ultrasonic tone to be heard by the cat.
Many of us like to feed birds in our gardens, but this often attracts the unwanted attention of a cat who will see your bird table or bird feeder as a fast food take-away. A cats motivation to catch birds can be far greater than the deterrent effect of any ultrasonic repeller. To help break the cycle of a cat repeatedly entering your garden, it is best to stop feeding the birds for a couple of weeks when you first install the repeller. By doing this, it will greatly increase the chances of the ultrasonic repeller having a lasting effect on the cat. Once the cat thinks that there are no more birds in your garden, the ultrasonic noise will then chase the cat away
The most popular model is the STV610 that has a range of 30ft.