Car Break-ins

Last Thursday we had two of our cars broken into right in our driveway. We know we locked both cars; nothing was damaged during the break-in. It was as if someone simply opened the doors, got in the cars without the alarm ever sounding. They looked through EVERYTHING inside; glove box was left open, EVERYTHING was spread out on the seats. We found both cars this way. There was  nothing obviously visible in the car calling for someone to break-in. They took NOTHING. Simply broke in and went through our things. I have another friend who reported the same a few months back and it was spooky to have that happen to us the same exact way. DPD told us we may have left the cars open and to be careful next time. We're left feeling helpless. I want to put this out there so if anyone else has experienced this maybe DPD can look into it.