I ordered a powerful green laser diode from eBay, wired it up and pointed it at some black paper, hit record on the camera, excitedly connected the battery and... nothing. I checked the wiring, all was good. I looked in the end of the diode, I could see a faint red glow inside, but nothing else. I must've got a dud unit.

Later I looked at the recording and my heart sank. When past me connected the battery, the room immediately lit up with a bright white glow. The diode emmitted an intense beam of infrared light... and I pointed that thing directly at my eye.

There wasn't a wider point to that, this just reminded me and I wanted to share. I suppose be careful of what you can't see.

I got lucky. That sort of thing can cause big problems. Especially those that stay unnoticed until old age. Hearing is also one of those.

Interesting stuff, I wish I had more time to learn about what they where doing.

We hear sounds when the cilia in the cochlea resonate with the incoming sound. We don’t have cilia of the length required to resonate with ultrasonic sounds, so there’s no danger of hearing loss.

Animals may get their hearing damaged, if they are in the path of the sound, are close enough that it’s still ultrasonic at their location, and are sensitive to the frequency used, I believe. Maybe someone who knows for sure can say for sure.