We just bought an ultrasonic humidifier. While researching if I needed to use demineralised water, I came across a website (this one, in German) saying that ultrasonic humidifiers are harmful/annoying for pets, as it emits a sound humans cannot hear but animals can. I just turned it on a few minutes ago, to see what their reaction is. They have been very curious, but it's hard to tell if they find it annoying (or will do so if they hear it for a longer time). I haven't been able to find any other sources regarding ultrasonic humidifiers and pets. Does anyone know if I can safely use it?
Edited to add: I had the brilliant idea to do another search, this time in English and not in German. I found a few websites saying that it depends on the frequency - cats can hear frequencies from 55 Hz up to 79 kHz, any ultrasonic device should use a higher frequency than that. This prompted me to email the producer of the humidifier with the question which frequency this specific humidifier uses. Nonetheless I would be curious if there's anyone with experience regarding this topic.