This question already has an answer here:

"TouchID requires your Password after 48 hours"

Update July 2016
Since posting this question, the message has changed to
Your passcode is required to enable Touch ID
& now has a documented answer at https://apple.stackexchange.com/a/245796/85275

I just spotted the above message for the first time today. I've had the phone 3 weeks [new 6s] & never spotted it before.

It's not something I need to 'fix' but I wonder if anyone knows what may trigger it; & why it took 3 weeks to ask me for the first time.

.. or, incidentally & totally opinion-based - why it thinks a 6-digit code is more secure than my fingerprint.

Late thought:
Does it do it 2 days after a reboot or OS update?
It's done it just one more time, which was perhaps 48h+ after the 9.1 update.

Current guess is it's "new to iOS 9" which is why people have been seeing it on older devices too.
I'm still convinced I get it once after every update - but it's something I just dismiss without thinking until later, when I've lost the train of thought that would allow me to 'accurately guesstimate' when it was last rebooted.

marked as duplicate by Mark, Community Jul 13 '16 at 18:12

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • It triggers if you haven't unlocked the device during the last 48 hours. Either keeping it unlocked or locked for longer will trigger it to ask for the passcode the next time it's unlocked. Most of the time that doesn't happen, at least for me. I also wonder why a 6-digit code would be more secure than my fingerprint... – Lizzan Oct 16 '15 at 9:53
  • I've unlocked it many times in the past 48 hours, as it locks as soon as the screen goes off with TouchID enabled; best guess is ~10 hours since I last looked at it [overnight]. Same user pattern as since new, it would be extremely rare, if not 'totally unthinkable', for me to not have looked at something on it at least once per day. – Tetsujin Oct 16 '15 at 9:59
  • Hmmm, I'd guess at a temporary glitch, then. – Lizzan Oct 16 '15 at 10:03
  • Weirldy enough, both my iPhone and iPad have glitched in the same way since I wrote that comment. – Lizzan Oct 17 '15 at 6:26
  • Just wanted to confirm I also saw this error message for first time Like OP, but on 1 yr old iPhone 6 with no change in use pattern. The only thing that might have been different was unusual background battery drain to below 20% for the first time in many months, plugged in to recharge last night, checked this morning after 7 hrs and got the message. – Jolo Oct 18 '15 at 11:47

The first part of your question has to be a glitch. The iPhone 6S is still a little buggy; mine doesn't always play system sounds, like the Siri chime and the lock "click" sound. But I can explain the second part of your questing:

Apple thinks that a passcode is more secure than TouchID is due to the fact that the odds of TouchID giving a false-positive are 1 in 50,000 (stated by Apple). However, the article hasn't been updated after the 2nd-Generation TouchID in the iPhone 6S came out, and given its great speed improvements, I would assume that the 2nd-Gen has a lower chance of giving a false-positive than the 1st-Gen. The odds of guessing a 6-digit passcode, would be literally 1 in 1,000,000. Even the odds of guessing right with 5 guesses, 1 in approximately 200,000 is still higher than TouchID. I like the convenience of TouchID and will still use it everyday, but from a purely statistical standpoint, a passcode is much more secure.

  • Re the Siri 'chime' - strangely if my phone is on Apple CarPlay, I get the chime [via the CarPlay system, not the phone itself], but not if stand-alone. My partner's 6s is the same. Re the 'real' part of the question - as I'm actually using just a 4 digit code, then the fingerprint is more secure; even less reason for it to trigger the 48h rule. – Tetsujin Oct 16 '15 at 12:43
  • @Tetsujin I'm guessing the Siri chime activates on CarPlay (and when otherwise connected to power and using "hey Siri" - at least mine does) to let you know that it has activated without you needing to look at the device. – Lizzan Oct 17 '15 at 6:30
  • 2
    A passcode might well be more secure in general, but when in a crowded place anyone could read that passcode over my shoulder. They'd have a harder time copying my fingerprint. – Lizzan Oct 17 '15 at 6:34
  • The odds of guessing a 6-digit passcode are 1 in 1,000,000. You count the correct one when calculating probability (e.g. ½ chance of guessing a true/false question correctly) – Arc676 Nov 5 '15 at 13:43
  • @Arc676 I know that one counts the correct number in the odds, I just forgot about a combination of 000000, but thanks for catching that, it is 1 in 1,000,000. – RedEagle2000 Nov 5 '15 at 22:15

The passcode superseeds the TouchID, the AppleID-password superseeds the passcode.

There's (arguably) nothing wrong with old styled passcodes. TouchID was not created because it's better than passcodes, it was implemented because it was just faster, more easy and convenient.

Hence the fact you cannot turn off the passcode, but you can turn off the TouchID. If you chop off your fingers, you still can enter your phone using the passcode (though I admit it would be significantly more difficult physically). If you lost your passcode, you still can reset it via iCloud.com.

The fact you have to re-enter your passcode (and on other occasions, your Apple ID password) after reset or 48 hours, is Apple's way to help you not forgetting those.

This is my personal view - but if you're looking at it like this, IMHO it makes more sense.

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