James Cook, writing for Business Insider:

Apple has filed a patent for a method to secretly enter “panic mode” on an iPhone when it’s unlocked with a specific finger. That could mean that the phone locks out personal information or completely resets the device.

The Apple patent, dated May 5 2014, includes lots of different potential functions for panic mode. Basically it’s a system to lock down the phone if a user is forced to unlock it with their fingerprint.