Scarecrow and CatStop
For the person who asked here's the Scarecrow and here's the CatStop and here's the link that explains what they do!
Basically, the Scarecrow is motion activated - anytime a cat (or anything for that matter!) walks into your yard, it will spray water at the cat. The Cat Stop on the other hand has an ultra sonic noise that only cats can hear (though some other animals may be affected). When a cat walks into your yard, it activates the noise which is annoying to the cat and keeps it out. However, one thing to note - if the cat happens to be deaf or hard of hearing, it will not keep the cat out.