iOS: Your passcode is required to enable Touch ID Occasionally, when unlocking my iPhone or iPad, I get the following message:


  Your passcode is required to enable Touch ID


Now this is not after a number of failed attempts or turning the device off. The device was used within the last 12 hours. Two of the devices are less than 2 months old, and one is a year old. Everything is up to date. It appears to be happening more-or-less at random.

Does anybody know why this message might appear?
There are certain rules that iOS uses that govern when your iPhone will prompt you for your passcode, and one of these relates to an 8hr period during which Touch ID has not been used. That alone would explain the scenario in your question (i.e. some nights you’re getting 8+ hrs of sleep, and other nights you’re not).

All of the Touch ID rules can be found in Apple’s iOS Security Guide. In summary though, the rules governing when a passcode is required instead of your fingerprint, are as follows:


The passcode has not been used to unlock the device in the last six days
Your fingerprint has not been used to unlock the device in the last eight hours 1
You have just powered up (or rebooted) your device
Your device has not been unlocked for more than 48 hours
You’ve unsuccessfully tried to use your fingerprint on five consecutive attempts
Whenever you add a fingerprint to your Touch ID settings
Your device has received a remote lock command


Regarding that last point, this refers to iCloud’s Lost Mode function. For more info you can read iCloud: Use Lost Mode.

See more details: http://www.macworld.com/article/3072181/ios/new-touch-id-rules-why-you-have-to-enter-your-passcode-when-you-wake-up.html

1 This is most likely the cause in your situation most of the time.