If you're looking for a new way to keep cats off kitchen counters or regularly mist the plants, Tinkernut's auto-triggered squirt-bottle hacks may work for you. One's easy to make, the other's high-tech but more functional.
The main trick, shown in the video above, is an Arduino-powered squirt bottle that also uses a motion detector to fire rapidly every time there's some motion in front of it. If you're trying to keep the cats off the counters, this is the perfect setup to keep in the corner behind the blender so the felines receive a quick, harmless spray every time they jump up. The second is built using an automated air freshener, which makes it cheaper but less effective.
Both projects are a lot of fun, and you can pick and choose which one works best for your needs. Hit the links below for full walkthroughs of both, along with all the parts you'll need.