After installing the program, press [win] - L to lock a laptop computer. This software emits a loud alarm sound when the locked computer is disconnected from the AC power. For example, someone unplugs the laptop AC power cord.
To unlock the computer enter a correct Windows login password. When the computer is unlocked, the alarm sound will stop.
For the best result, do not allow your computer hibernate or standby automatically while it is running on AC power and user account must be protected by a password.(via)