HP ProBook 640 G1 Maintenance And Service Manual page 22

Component
(3)
(4)
(5)
12 Chapter 2 External component identification
Wireless button
Volume mute button
Fingerprint reader (select models only)
Description
Turns the wireless feature on or off but does not establish a
wireless connection.
Mutes and restores speaker sound.
Allows a fingerprint logon to Windows, instead of a password
logon.