HP ProBook 640 G1 Maintenance And Service Manual page 20

Component
(6) Internal display switch
NOTE: The antennas are not visible from the outside of the computer. For optimal transmission, keep the areas immediately around
the antennas free from obstructions. For wireless regulatory notices, see the section of the Regulatory, Safety, and Environmental
Notices that applies to your country or region.
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10 Chapter 2 External component identification
Description
Turns off the display or initiates Sleep if the display is closed while
the power is on.
NOTE: The display switch is not visible on the outside of the
computer.