Background agent that locks the screen when it detects that someone typed a specific word.

People who leave their computer without locking the screen are exposed to a prank by their colleagues to remind them that they should secure their PC more thoroughly.

The prankster will use the victim's machine to post to IRC or a Facebook status something like "I love to eat Jello!" (the wording is often different, but the word 'jello' is always in there. I don't know the origins).

To secure against this, the app examines the keyboard input stream and if it detects that someone has typed the magic word, it immediately sends the computer to sleep, which also locks the screen and locks the prankster out.

It's pretty simple. The main loop hooks into the global keyDown event stream.

Internally, there is a state machine that looks for the next character in the magic word. (Repeat consecutive letters are ignored). As the user types, the state machine will either progress towards the end, or reset if the wrong character in sequence is pressed. If it reaches the end, the lock is activated.

It supports pressing backspace, and also repeat characters (so someone can type 'jeeeellllooo' and it will still activate).

Just run it. To monitor global key events, the app must be whitelisted in OSX's "Settings > Security & Privacy > Accessibility" section. If it is not, the app will warn you about this and open the dialog for you to add it. You'll need to restart the app after you do this.

Navigate to "OSX Settings > Users & Groups > Login Items" and add the application.

Open JelloDetector/AppDelegate.m and edit the characters 'j', 'e', 'l', 'o', and make sure MAXCHARS is the same number of characters.