For better security, you can set a passcode that must be entered each time you turn on or wake up iPod touch.
Set a passcode. Go to Settings > Passcode and set a 4-digit passcode.
Setting a passcode turns on data protection, using your passcode as a key to encrypt Mail messages and attachments stored on iPod touch, using 256-bit AES encryption. (Other apps may also use data protection.)
Increase security. Turn off Simple Passcode and use a longer passcode. To enter a passcode that’s a combination of numbers and letters, you use the keyboard. If you prefer to unlock iPod touch using the numeric keypad, set up a longer passcode using numbers only.
Allow access to features when iPod touch is locked. Go to Settings > Passcode. Optional features include:
Siri (if enabled; see Siri settings)
Passbook (see Passbook at a glance)
Reply with Message (see Make and answer calls)
Allow access to Control Center when iPod touch is locked. Go to Settings > Control Center. See Control Center.
Erase data after ten failed passcode attempts. Go to Settings > Passcode and tap Erase Data. After ten failed passcode attempts, all settings are reset, and all your information and media are erased by removing the encryption key to the data.
If you forget your passcode, you must restore the iPod touch software. See Restore iPod touch.