PawSense!
PawSense: "Even while you use your other software, PawSense constantly monitors keyboard activity. PawSense analyzes keypress timings and combinations to distinguish cat typing from human typing. PawSense normally recognizes a cat on the keyboard within one or two pawsteps.If a cat gets on the keyboard, PawSense makes a sound that annoys cats. This teaches your cat that getting on the keyboard is bad even if humans aren't watching."