You may have misunderstood. Ultrasound is not being used here to deliver power to these 'sensors'. The devices give off distinctive ultrasound noises when they are bashed by things, like little cymbals. They are not really sensors - they transduce a mechanical input to a high-frequency mechanical output. To be used as a sensor you need a microphone and (typically) an AtoD as well.

Since it's just a little signal, there's very little power in it, so while your pet might hear it, and maybe it'll cause your noise-canceling headphone to squawk, it's not going to have enough energy to hurt anything.