Here is a very cool gadget called Lockitron. Though I've ordered it, I haven't gotten a chance to use it myself. It's as simple as placing the Lockitron over the deadbolt on your door! It connects to your phone, so you can lock and unlock your door from anywhere and you can share the ability to operate the door with your friends and family, all without seeing the device from the outside of your house. You can choose to get a message anytime the door opens (useful when your'e on vacation) and the best part? The device has Bluetooth so you can simply walk up to the door and it unlocks for you.
It's available for pre-order (shipping in May 2013).