There is talk on FB that the board the second chap has is picking up a key frequency. I dont know how true it is.

Simple key coder is also being talked about.

Best prevention is a better alarm with more sensors. You could also install manual kill-switches, disabling fuel pumps, hidden in place difficult to locate in the 2/3 minutes of an attempted robbery. Also have a tracker installed. For the sake a few hundred quid is another piece on your side of the court. Also could have an anti-theft poll installed in front of the car.

Disgraceful that you have to go to this measures to keep your property safe.