If you're tired of forgetting your keys—or your roommates forgetting their keys—get the GSM doorbell and you'll never have to worry again. It mounts onto your door, and when rung, calls a pre-programmed number. Punch in a key-code in your phone and the door unlocks automatically. Never get up from your chair again.
Also, this new version lets you call the device to unlock it directly without having to ring the bell. You can phone your door as you approach your home so it's unlocked when you get there. This sounds pretty damn convenient if we don't have to spring for a calling plan for the doorbell.