saw this on

a bbc program mainly about the ''faked rear end accidents' issue.

On that, they spoke about people stealing from cars during the night, but leaving one of the devices on so that people think they've locked their cars , but actually haven't. They showed a woman who'd been very suspicious as she kept coming back to the car unlocked after thinking 'i'm sure i pipped it' when she spoke to neighbours, they'd been robbed with the same 'but I was sure I locked it'

Basically , CHECK it's actually locked by pulling on the handle if you're not sure...

iirc, it's some gps jammers that are legitimately sold in other countries, but can be bought on ebay for peanuts that can work...