This has been posted before, but according to professional car thieves that were being interviewed by one of the TV news magazines (60 Min., 20-20, or Dateline), the most effective device was a delayed fuel shut off valve. They said a car that had no outward appearing alarms, club. chains, etc. but would die on them when they got onto a public street was one they immediately had to abandon because one just couldn't stick around with a stolen car. Might cost the owner a wrecker and pound fee but that's better than a total loss.
