I only expect they make other people choose when they are around to have this on. We used to do lots of experiments in the lab with ultrasonics, playing around

I only expect they make other people choose when they are around to have this on. We used to do lots of experiments in the lab with ultrasonics, playing around. A couple of times we had our ears hurt for a while(all the people in the team) after getting out of the lab, We learned the lesson, even when you don't hear anything, it can affect you. In fact, it is worse when you can't detect something that could affect you. I would prefer to use something that I could see like visible green light and solar cells in the phone. I won't put my eyes too near of a 10Watts source, but with something you can't see or hear, you could inadvertently put your organs too close for too long.