Tom, I think London Fire and Rescue service (yes that is there real title now but they still aint using it!) have been wearing these devices for a while. They are meant to wear them everytime they are off station, and are as you said for an early warning device type thing. Great idea in practice, but its gotta be costing the governtment a fortune if they are thinking of fitting out every fireman, woman, ambulance person, copper, hospital worker, mobile salesman, quaker, baker, candlestick maker... Tad OTT dont you think!