A Bluetooth headset has a transmitter inside it in order to send your voice signal to the mobile phone. The difference is that it typically has a transmitt power of 0.001W (some may have 0.01W?), where your mobile phone has a maximum transmit power of 2W (in GSM). It is a difference of 2000 times.

If you think that the risk is dependent on the power level, a Bluetooth headset is probably safer than the mobile phone itself. If you think that any transmitter is unsafe close to the head, Bluetooth is not the answer. Use a classic "wire" handsfree instead.

I'd disagree that the wired earpiece would likely be safer that Bluetooth -- Depending upon what lab is doing the testing, an earpiece has been found to conduct between 20-50% of the radiation from the handset to the ear.

There was even a British study done a few years ago and reported in something called "Which? Magazine" ( Google it for more details ) that claimed that the radiation was concentrated more by the ear piece into a smaller area, thereby creating 300% of the SAR of the handset alone.

There were subsequent tests done that claimed that alarming test was doing using flawed methods though ( in any case, the retest is reported at [Only registered and activated users can see links. ] if anyone really wants to delve deeply. )

But in any case, I'd think that a Bluetooth transmitter, emitting less than 1% of the power of a cellular handset would be a safer bet than either a handset or a wired earpiece. But that's just an amateur hunch. Keep an eye out for the SAR reports on the bluetooth headsets. Since they are expecting to sell over 100 million Bluetooth phones next year, I'm sure they will be tested.

1. I trust scientific/technical publications a lot more than "Which!"-magazine, and they do not confirm the measurements. The common view is that the Which!-study has been thoroughly discredited, and furthermore no one has been able to replicate it. (The rise has, AFAIK, only been found in the measurements by the Which! magazine)

2. The article "report75" for example, does confirm that wire headsets do not give rise to the SAR level.
Quote: "Indeed, even using the personal hands-free kits under the worst conditions identified, they still offered large SAR reductions compared to the case where the phone was held against the head."

3. Elecromagnetic field theory is very complex. Do not trust hunches too much...

4.BT devices do not have to be SAR-tested due to their low power output.