About half of the energy is gone in 15 feet. None remains at 30 feet. Even if the devices worked in the lab, the energy loss and shadow effects would make them useless in the real world. Insects and mice are good at hiding behind couches or overstuffed chairs. Subsonic devices have recently hit the market.
Manufacturers claim they are even better than ultrasonic ones.
Instead of sending out a high frequency signal, they produce a low frequency sound or vibration. Some are emitted directly from a speaker in a little black box. Of course, the little red light is on to show you it is working because you can't hear the sound. Your pets, of course, are not supposed to be harmed. The most ingenious subsonic devices are those used in agriculture.