Summary Box: Texting poses risk to alarms, devices

THE THREAT: Computer hackers can force some cars to unlock their doors and start their engines without a key. They can also snoop at where you’ve been by tapping the car’s GPS system.

HOW IT’S DONE: Car alarms, GPS systems and other devices are increasingly connected to cellular telephone networks and thus can receive commands through text messaging. That capability allows owners to change settings on devices remotely, but it also gives hackers a way in.

NOT SO FAST: Actually stealing a car wouldn’t be so easy, and the techniques shown are limited so far to lab environments.