04 Chevy Malibu won't unlock

I've got a 2004 Chevy Malibu and all of a sudden the keyless entry won't unlock the car. The key also won't unlock the door. When I hit the lock button the security system will beep once, and when I hit the unlock button it beeps twice, but the door won't unlock.

I couldn't find anything in the users manual regarding this, but I assume this is an issue with the security system? Does anyone have any ideas how I can make my car work again?