That’s easier. Just measure weight. When the weight goes up, and then comes down again, a cat has gotten into the litter box and probably done some business. Th

That’s easier. Just measure weight. When the weight goes up, and then comes down again, a cat has gotten into the litter box and probably done some business. Then you can activate automated systems to remove whatever has been deposited. This method also lets you track the weight of the cat, effectively for free. If you have multiple cats, then you need an RFID reader that either reads the chip you had inserted into their body, or an RFID chip that you put onto a tag on their collar. If you’re more concerned about being told when it’s time to change the litter box because it’s too stinky, then you’re going to need to measure the stink. Power from urine could work, but you’d need to capture that before it gets absorbed by the litter, otherwise you couldn’t measure it or generate power from it.