Handicapping Killer Cats
Not meant for mousers.
One of the significant differences between cats and dogs is that dogs usually don't drop off their prey - mice, birds, lizards - on your doorstep. A new, nature-friendly collar for cats would keep cats from doing the same. This collar would have several small lights built into it that would blink every 30 seconds or so. Powered by a watch-type battery, the lights could blink white or any other color of your choosing. Their flashing would serve to warn potential victims that a predator was in the area, giving them time to get away. It'd be frustrating for the cat, but it would also help guarantee a positive outcome for both the prey and your doorstep.