Once your alarm has been set off, your computer will sound a loud alarm and prevent the system from being muted or put to sleep. Lockdown will take a snapshot of the offender using your computer's built in iSight and, if you've entered your e-mail address, e-mail the snapshot to the account of your choice.
Using your Apple Remote, you can arm and disarm Lockdown from anywhere in the room. Simply start the application and hold down the "Menu" button on your Apple Remote to arm the system. Hold down the "Menu" button once more to disarm it and resume using your computer.