An "electronic" cat deterrent sounds fearsome, but in fact these devices are completely harmless to cats and other animals. They have the advantage that whereas powders & chemicals have to be re-applied over and over, an electronic system will last for years.
How do they work?
Most electronic deterrents work by emitting an ultrasonic alarm triggered by a motion sensor. The key to it is that the sound is inaudible to humans, but cats, with their better hearing, will be startled and frightened away by the sound. Although the sound the cat hears is an effective deterrent it is in fact harmless to both them and other animals.
This device uses a 9-volt alkaline battery or is adaptable to 9-volt adapter operation . It uses minimal power and indicates when the battery is low. The CatScram will guard a 6-foot range on the floor or flat surfaces and up to a 15-foot range or more when elevated or tilted
The Contech "CatStop"
The CatStop has a detection range up to 20 feet and will protect an area up to 330 square feet. The unit can be expected to operate for up to nine months on one standard 9 volt battery (based upon 4900 activations spread over 245 days at an average of 20 per day)
The Lentek "Yard Contro+"
This system uses ultrasonic and audible sounds combined with a startling, pulsating strobe light to deter animals from entering the coverage area. The Lentek "Yard Contro+" features a weatherproof design & easy operation. It is activated by motion within a 360°, 30 ft. radius and operates on four “D” batteries
The Weitech "0051"
The 0051 Yard and Garden Protector uses multiple frequencies. This means that you can customize the settings to repel specific common yard pests. A built-in motion detector activates the unit when the unwanted pest enters the protected area. The unit is easy to surface or pole mount with the included mounting brackets. The Model 0051 is powered by 4 "D" cell batteries.