Yealink SIP-T48G User Manual page 73

If it is set to other values except 0 (e.g., 5), the phone will be locked when the phone is
inactive in idle screen for the designated time (in seconds).
Tap the Save soft key to accept the change.
5.
When the phone is locked, the touch screen prompts "Phone locked." and displays the
icon .
To change the phone unlock PIN via phone user interface:
Tap ->Basic->Change PIN.
1.
Customizing Your Phone
59