Headsets and other bluetooth devices only need to broadcast 20 meters (max) or so, less than 2 KM for cellphones and PDA"s such as blackberries. As a result the batteries required are much smaller, therefore the intensity of the radio waves is greatly reduced.

It's still a worry, but your talking orders of magnitude less than that of a cellphone. Best get rid of the cellphone if you are that paranoid. =)