Apple's upcoming iOS 11 has a feature that lets you quickly disable the iPhone's Touch ID fingerprint scanner, forcing you to use a passphrase to get into the phone.

The feature, spotted on Twitter and reported on by The Verge, is actually a way to quickly call an emergency number, and is accessed by rapidly clicking the home button five times. But after you've done that, the only way to access your phone again is by typing in your passphrase (assuming you've set one).

There were ways to disable Touch ID before; for example, rebooting the phone or scanning the wrong finger a few times will do the trick as well. But this is arguably the fastest way to disable Touch ID, which is important as officers of the law can force you to give up your fingerprint, but (ideally) cannot force you to give up your password.

iOS 11 is a game-changer for Touch ID. Press power button rapidly 5 times and it opens the 2nd screen, but it also forces passphrase entry! pic.twitter.com/uvWbM04lyk — Kia‏☆ (@alt_kia) August 17, 2017

And with rumors that the upcoming iPhone 8 will have face recognition instead of a fingerprint scanner — one that works even when you're not directly facing the phone — this could be a good way to make sure your phone cannot be easily unlocked.

It's hard to say whether the feature was intended to be a "cop button," as some folks on Twitter have dubbed it, but as far as security goes its value is dubious at best. If you try locking your phone in this way to avoid airport screening, the authorities will likely assume you've done it on purpose and then you'll likely have to spend hours explaining what, exactly, was it that you needed to hide. And it's easy to imagine many cases in which you wouldn't be able to quickly tap the home button five times. So if you're worried about security, the best thing you can do is disable Touch ID altogether and use a password instead of a simple PIN code.

Apple's iOS 11 is currently available as beta, and it's likely to be released in September.