A grey area for the boys in blue

Three million of us use radar detectors to beat police speed traps. Are they legal, and do they work? Yes and no. By Phil Llewellin and Penny Jackson

The Cobra Trap Shooter sat on my dashboard winking and bleeping madly. I was obviously about to arrive in a veritable nest of police speed detectors and should brake smartly. In fact I was stuck at the entrance to the Blackwall Tunnel, the Thames crossing where any movement at all is a miracle.

This was my third day of driving around with a gadget that looks like a cross between a computer mouse and part of a mini-cab radio system. And it was proving more of an irritation than an aid. I had not come across one speed trap, unless the police had taken to operating from suburban garages and stationary traffic queues.

The detector was as simple to install as the instructions had promised. Plug the connecting wire into the car cigarette lighter socket, switch on the Trap Shooter and it's all systems go. I pressed the button which put it into city mode to cut out any extraneous radar interference in urban areas. If you don't do that, it is like sitting in an air-traffic control tower as the detector will even pick up a signal from an electrically operated door.

What I had really been hoping for, though, was evidence of the 360 degree protection provided by the omnidirectional laser where it really matters, on the open road. I wanted to be able smugly to breeze through a radar trap at a precise 70 mph. But after a couple of fruitless journeys on A roads, I returned to town. The only warnings the detector gave were of cameras that perch on traffic lights.

At least there I could see how the system worked: as the car drew closer to a camera, so the detector's warning lights moved from amber to red and the bleeps grew more frantic as the signal strength increased. As I passed the junction, the intensity of the lights decreased. Rather a lot of noise about nothing, although it made me think twice about sneaking through on amber.

It also gave me pause for thought on the ethics of using the detector. I felt I had not been driving faster or any less safely with it in the car. And wasn't its deterrent effect similar to the signs police frequently display about entering speed camera zones?

In the US states where the detector is illegal, the whole business has become a hi-tech game of cat and mouse. The police there use a VG2 gun which can detect radar detectors. So some models now incorporate digital Stealth VCO - a spin-off from the technology of its aeronautical namesake - which reduces the level of electronic leakage.

At a starting price of pounds 189 it would seem cheaper to stick to the speed limit. PJ