If you're interested becoming afraid around your cars, some of my security friends at the University of Washington have been busting up cars for research: http://www.autosec.org/faq.html
Of course, their exploits are a bit more complex and involve various side channels and hardware vulnerabilities, while the keypad issue can be executed by someone just typing in numbers with their fingers.
This paper is particularly in depth and interesting: http://www.autosec.org/pubs/cars-usenixsec2011.pdf
Of course, their exploits are a bit more complex and involve various side channels and hardware vulnerabilities, while the keypad issue can be executed by someone just typing in numbers with their fingers.