Secure your mac with your bluetooth-enabled phone, auto-lock it when you're away.

Some time ago i though about security of my laptop. When I'm not at home, at work, for example, i often go away from my macbook and wanted to be sure no one will look at my screen when i'm away. I'm running mac os x, so i found free Proximity app. Get it here
Create new file and type it's full path in Out of Range Script field.
/usr/local/bin/screensaver.scpt

tell application "System Events"
    set ss to screen saver "Random"
    start ss
end tell

All done, now you can walk away from your mac and when you're back - mac is protected with screensaver.