Our car was broken into overnight a month ago with the same MO - I'd left it locked and found the doors open in the morning. The police told me that thieves are now using a device on cars with remote central locking that scans all possible signal frequencies and can eventually unlock all those cars.

They told me there had been a number of these crimes in SE23 and beyond recently, so it turns out that locking your car is of little use in these circumstances. The only prevention suggestion they made was to fit CCTV and point it at the car. Doesn't seem to be much that can be done as most cars use this locking system these days.

I was just grateful they hadn't smashed a window to get in...