Compaq 247320-003 - Deskpro 4000 - 5166 Model 2500/CDS Reference Manual page 42

To reattach the Smart Cover Lock, secure the lock in place with
the three tamper-proof screws.
QuickLock/QuickBlank disables the keyboard and mouse
interface, and can blank the screen, without exiting application.
To enable the QuickLock and QuickBlank features, complete
the following steps:
1. Turn on the computer.
2. When the F10 Setup message appears in the lower-right
corner of the Compaq logo screen, press the F10 key.
If you do not press the F10 key while the message is
displayed, you must turn the computer off, then on again
to access the utility.