Truvelos - at least those in Kent - do flash.

As do the ones on the A45 between coventry and Rugby.

I've set them off a fair few times

DRJ i used to work in Halfords....they did a special deal at one point where members of staff were allowed to buy 1 for half price, I used it for 6 months till the 6 months free reg ran out and then sold it on ebay for