How does bluetooth work?

15 November 2016


Using a mobile phone



How does bluetooth technology work? Could it be harmfull to us if our phones are continuously "bluetoothing?"


We put this question to tech investor Peter Cowley...

Peter - Yes, how does bluetooth work? I mean, there's obviously a very complicated answer to that which we won't go into now but, in principle, it's the same as any other form of wireless based communications. Same as wifi, same as mobile communications where something's transmitting one end and something's receiving the other end. Unlike a radio and television where the receiver doesn't transmit back again, it does, so they're talking to each other all the time. It uses the same frequency as wifi which is 2.4 ghz, which is a band that's open to the whole world. But the big difference between that and wifi and mobile comms is that the power output is very, very much less. So if you take the call power of a modern smartphone the absolute maximum it can transmit at is 2 watts and it's usually about 250-500 milliwatts, so that's a quarter to half a watt. And bluetooth is about 1-2 milliwatts, so it it's about 250 times less

Now there's some interesting statistics here which I think those with a medical bent i.e. Chris will be quite interested in. Apparently, the brain will get damaged if there's at least a 4 degree increase in temperature and, if you're on the phone for 20 minutes, your ear increases by - and this is research that's been done so don't worry I'm not making up - about 0.3 degrees centigrade. And the brain, just inside the ear, by 0.15 degrees centigrade. And that will stay stable then, it's not going to increase for every 20 minutes once it's on so once you've had a 4 hour call.

Chris - Cumulatively.

Peter - And, just out of interest, the other way round. Some people may know that if you type a certain number in on the phone you can actually measure the signal strength wherever you are and that works out at home, my home where I get about two bars about a billionth of a watt so the amount of power coming through the local cells transmit is very, very small.

So, to finish answering the question - bluetoothing very much less powerful than a mobile phone. As he says it's on all the time but it's not on the whole time. The only time it will be transmitting backwards and forward, or certainly in one direction, is when you're listening to something, say an earpiece in your ear which is then bluetoothing at the same time. Otherwise it's occasionally polling, which means checking if there's anything out there, perhaps once a second or something like that. So there's very, very little power there that's being transmitted. So don't worry.


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