Users must now enter a passcode anytime the device’s Touch ID fingerprint sensor hasn’t been used in the past eight hours or when the device hasn’t been unlocked with a passcode in the last six days. In such cases, Touch ID is turned off until users enter passcodes.

Apple-tracking site Macworld noted the little-noticed change and investigated the reason behind it. It found users who claimed that Apple’s passcode requests had become increasingly frequent.

Apple has long required that users enter passcodes to unlock devices in certain cases. For example, users had to do so after they rebooted their iPhone or iPad. But the requirement, for some unknown reason, had become more routine.

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Earlier this month, Apple had published a tweak in its iOS security guide that mentioned the more stringent security feature, causing some to believe it was new. In fact, the limitations on Touch ID were actually implemented when Apple (AAPL) introduced its latest operating system, iOS 9, last year. But without any public mention, few people had noticed, although some users and security experts had recently talked of having to enter passcodes more frequently in their iPads and iPhones.

Apple declined comment to Fortune about the change.

The new Touch ID policy highlights the two ways of unlock Apple devices. Both potentially make it more difficult for law-enforcement to access data on devices as part of their investigations.

That was proven in the company’s battle earlier this year with the FBI over unlocking an iPhone 5c used by San Bernardino attacker Syed Farook. The FBI had asked for software from Apple that would help it unlock the device. After Apple declined, the FBI was able to find a way to unlock the device by using a tool supplied by an unidentified third party. The FBI has subsequently unlocked devices in other cases by circumventing some of the security features built into the iPhone and iPad.

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Earlier this month, Touch ID also came under fire after a Los Angeles judge ruled that a woman was required to provide her fingerprint to open her iPhone and allow FBI access to her data in connection with a criminal case.

In addition to Apple’s newly discovered eight-hour, six-day rule, the company also turns off Touch ID if a device hasn’t been used for more than 48 hours. It also requires that users enter a password if a device is restarted or if a user unsuccessfully tries to use Touch ID five times, among other rules. Those rules, however, were in place before Apple’s latest tweak.