We occasionally have to defend our conservatory roof from invading quadrupeds* and bought this magnificent beastie to do so. (Warning shots usually suffice)

L.
* a neighbourhood cat, it rather annoys ours by standing on the transparent roof.

I had one of these when I lived with my older sister and needed to keep her cats off the coffee table:

I used to call it my “extended-range water bottle”. And I usually didn’t have to shoot it, the sound of the water in the tank sloshing around was enough encouragement for the cats to Quit That Shit Out, Yo.
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Lime2K
The One True Evil Overlord