Interesting read on the potential to steal cars with passive entry/ignition keys:
http://www.technologyreview.com/computing/27037/page1/
Cliff's Notes: Thieves may be able to use inexpensive equipment to relay your fob's signal to unlock your vehicle and drive it away.
http://www.technologyreview.com/computing/27037/page1/
Cliff's Notes: Thieves may be able to use inexpensive equipment to relay your fob's signal to unlock your vehicle and drive it away.