https://arstechnica.com/gadgets/2017/08/new-feature-in-ios-11-quickly-and-temporarily-disables-touch-id/

Apple is slated to release iOS 11 to all users this fall, but with the public beta available for anyone to try, some previously unannounced features have been discovered. According to a report from The Verge, a feature in the updated operating system allows users to easily change settings so your fingers can't unlock your iPhone using Touch ID. Pressing the power button on an iPhone rapidly five times will bring up an emergency screen, allowing you to either call 911 services or enter a passcode to enable Touch ID. Until you enter that passcode, Touch ID won't unlock your device.