iOS/Mac: Don't want the hassle of typing a password on your Mac? Knock is an app for iOS and Mac that uses your phone or tablet to unlock your computer.
Knock uses Bluetooth to pair your Mac and your phone together. Then, when you tap on your phone two times, it sends a signal to your computer to unlock it and log in. Knock uses Bluetooth Low Energy so it doesn't suck up that much battery life when it's on.
It's simple, but it works surprisingly well.
Knock for iPhone ($4.49) [iTunes App Store]
Knock for Mac (free)