I was never totally convinced of the effectiveness of this in terms of how it repelled animals, but there was no doubt of its effectiveness at annoying my children.
Like this
https://www.bestpestcontrol.co.uk/ultrasonic-cat--fox--dog-repeller--adjust...
requires 4 x AA batteries (not included)
Battery powered ultrasonic cat/fox/dog repeller (Bishopston BS7)
This offer has been gifted to someone and is no longer available.