Bluetooth devices have 3 power classes, 1mW, 2.5mW and 100mW. If your device is 100mW one, its maximum allowable output is a tenth of a watt. If you stuck the antenna right up your nose, that's not enough power to wiggle water molecules more than a molecule or two deep, let alone "hurt" your brain.
At 2.4 GHz, bluetooth is just below the 2.45 GHz consumer microwave oven frequencies. Your 1100W microwave oven, with an efficiency of about 65%, outputs around 700W of RF energy. Now, that is enough to boil water and cook, but only if the water/food is inside a tuned cavity (the reason why they're all about the same size on the inside, only certain measurements of the interior will be a function of the magnatron's frequency wavelength). The weird habit of people assuming that there's something magical about radio waves that makes you sterile, see Elvis down at the grocery store, or gives you prostrate cancer is a lot of paranoid thinking.
I'll try to put this in perspective. A microwave oven is 7000 times more powerful than your bluetooth device or cell phone. If your personal handgun is 7000 times as powerful as a child's cork gun, you have reason to fear the handgun. The toy one, however, wouldn't do enough damage to kill a mouse.
I'm pretty sure that a 1500W ham radio within a couple of feet of the operator exposes us to horrendously more RF energy than a cellphone or bluetooth device does right against our heads. If this was damaging to the brain, I think we would have noticed it, by now. We'd be dropping like flies, or wandering the streets muttering crap about making America great again.
. I was thinking about going with a system that would have push-to-talk capability as well as constant communication like the Sena system.
