As far as i am aware they need to pull you over,they normally work in pairs , or as i found out last month jump out on you , yes i got pulled i was doing 33 in 30 zone , i got lucky maybe the charm of the two year old in the car saved me and i got ticked off after he had show me the gun.
So in short they ( if memory serves right ) need to pull you there and then and show you the gun / record as unless im very much mistaken it can't take a photo ( the gun that is ) and neither will it record your details. It's one point / check ( pull you or reset it for the next one )
maybe wrong