Sony PEG-TH55 - Manual (Page 206)

Protecting your data with a password 206
Locking your CLIÉ handheld with a password (Data protection)
5
Tap [Lock & Turn Off...].
The System Lockout screen is displayed.
6
Tap [Off & Lock].
Your CLIÉ handheld turns off and locks.
To turn on your CLIÉ handheld, you must enter the correct password.