I picked up an app called Knock today. It is a simple app that allows you to unlock your Mac by knocking twice in rapid succession on your iPhone. Speaking as someone who has to type his password into his Mac many times a day, I thought it might prove useful (if slightly extravagant).
My wonderful , not-at-all-sarcastic friend Gabe suggested that, instead of spending the $4 on the app, I “knock” on the keyboard with my fingers and type in my password, saving a little money towards retirement in the process. It should be noted, however, that this is coming from a guy who spent $70 on a text editor that makes you change configuration settings by editing a 4000 line text file.