The M90s output much less radiation than my Bose Soundsport bluetooth earbuds. But they still measure highly when within 1" of the antennae of the meter. Specific numbers below.
The meter (Gigahertz Solutions HF-35C) is not meant to be used in such close proximity, so I don’t put a lot of faith in the signal strength numbers. I just wanted to understand whether or not they are constantly transmitting or only transmitting when streaming, and the answer seems to be: constantly.
I made a video of my measurements here: https://youtu.be/zGUXy2yJYSA
I took all measurements in “peak” mode, which means it’s displaying the highest burst that occurs over a brief interval rather than the average output.
The M90s are non-detectable from 6 inches away. But at 3" they measure at around 50 uW per meter squared. When I bring them to within 1 inch from the tip of the antenna, the reading is 150 uW per meter squared when not streaming, and 350 when streaming. When I put them within millimeters of the antenna, it’s 600-1400 while non-streaming and over 2000 (max detectable threshold) while streaming.
By comparison, my Bose Soundsport bluetooth headphones (earbuds tethered by neck cord) measured at 700+ uW from 6 inches away and over 2000 uW from 3 inches when streaming. So the Bose at 6" away is the same strength as the M90s at around half an inch away. Clearly the M-90s are much lower energy than the Bose. But I wear them 16 hours a day, so that’s something to consider.
And my phone during a phone call was much, much higher: over 2000 uW from 4 feet away, and around 1300 from 5 feet away.
Even worse: my wifi router exceeded the 2000 uW threshhold from 7 feet away, and my microwave oven exceeded it from 12 feet away! If you’re worried about this stuff, don’t stand in front of your microwave, and don’t keep your router in the same room where you sleep or work!
Most of the sites discussing the dangers of bluetooth are from people selling books on how to minimize your exposure, so I put little faith in them. The 200+ scientists who signed the letter urging action are more believable, but they are not even close to any kind of a scientific consensus (in sharp contrast to, say, the consensus about climate change). Here is a good summary article that talks about some of the possible dangers other than cancer: https://www.sciencedirect.com/science/article/pii/S0013935118300355
Here is a paper discussing the possible link between microwave exposure (e.g. via bluetooth) and alzheimer’s: Microwaves and Alzheimer's disease - PMC
The more you look, the scarier it gets…
But I LOVE my Marvels!!!