http://www.knocktounlock.com/ http://www.knocktounlock.com/ comes to mind. Edit: Sorry, it appears Knock can't actually lock your Mac. Airlock promises that fu

http://www.knocktounlock.com/ http://www.knocktounlock.com/ comes to mind. Edit: Sorry, it appears Knock can't actually lock your Mac. Airlock promises that functionality though - so that might be of interest to you.