This article explains how to turn PEPPER OFF:

Regular TURN OFF:

Put a hand on its shoulder or its back, in order to keep it in position. Press and hold the Chest Button until the robot says “GNUK GNUK” (~4 seconds).Note: If the Autonomous Life is running, Pepper goes to its rest position. The shutdown process is completed when all the LEDs are off.

Forced TURN OFF

Use this if Pepper does not turn OFF normally with the regular Turn OFF,

• Make sure Pepper is in a safe position, or he may fall because the motors will switch OFF suddenly !
• Press and hold the Chest Button for 8 seconds.

Result:

• the robot says “GNUK GNUK”,
• the shoulder and ear LEDs fade quickly.