Biometrics are an incredible convenience that lets you unlock your iPhone with your fingerprint. On iPhone 5s through iPhones 8, Touch ID lets you authenticate with your fingerprint. On iPhone X, Face ID lets you authenticate at a glance. But there will come times when you need security more than convenience. For example, when you're traveling through a sketchy area, crossing a border into a region you don't trust, or approached by people or agencies that may not respect your right to privacy. Previously, you had to reboot your iPhone to quickly force it to require your passcode or password for unlocking. With iOS 11, though, there's an even quicker way. Here's how!

Note: This feature is currently iPhone only. Hopefully, Apple will bring it to iPad as well.

How to have Siri turn off Touch ID and Face ID on your iPhone

There may be some situations in which you can't physically access your iPhone, but you still want to lock it down so that your finger or face can't automatically provide access to it. As of iOS 11.2, Apple added a secret message that will let Siri know to temporarily disable Touch ID or Face ID, forcing it to require a passcode or password to unlock. Just say (if you've got an iPhone X, don't look at the screen or it will unlock):

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"Hey Siri, Who's phone is this?"

Siri will respond with your contact card if it's assigned to you. At that moment, Touch ID or Face ID is temporarily disabled, requiring a physical code to access.

If you want further security, you can then say, "Hey Siri, Goodbye" to close the content on the screen, hiding your personal contact card from view.

How to quickly turn off Touch ID and Face ID on your iPhone

When Apple brought the SOS feature from Apple Watch to iOS, the company added a "bonus" feature: immediately, though temporarily, forcing a passcode or password to unlock.

On iPhone 5s to iPhones 7:

  • Click the Sleep/Wake (On/Off) button five times in succession.

On iPhones 8 and iPhone X:

  • Squeeze the Side button and either Volume Up or Volume Down

That's it. The Power Off/SOS screen will appear, and you'll have to enter your password or passcode to get back into your iPhone.

Why you might want to quickly kill Touch ID or Face ID on your iPhone

Most of the time Touch ID and Face ID will be the easiest and most convenient way to unlock your iPhone and get access to all your apps and data. But it can also make it easy and convenient for someone else, ranging from friends, family, and roommates, to significant others, flings, and one-night-stands, to criminals and government agents to get into your phone as well.

If you fall asleep, get drunk or drugged, or are otherwise rendered incapacitated or unconscious, anyone in the same room with you could touch your iPhone to your finger to unlock it. That includes roommates or dates you don't trust. Likewise, they could attempt to get you to look at your iPhone X to trigger Face ID.

If you're arrested, detained, held captive, or otherwise forcibly confined, anyone near you can force your finger onto the Touch ID sensor and unlock your iPhone. Although Face ID can require attention (your eyes and face looking at your iPhone) that might be forceable as well.

Most of the time none of us have to worry about those kinds of "nightmare" scenarios, but we should all still be aware of them.

When you might want to quickly kill Touch ID or Face ID on your iPhone

Just because you can quickly force your iPhone to require your passcode or password doesn't mean you should. The vast majority of the time, in fact, you're going to want to keep Touch ID and Face ID up and running.

You only want to consider disabling these convenient authentication methods when you're going into an area where you're not sure about your personal privacy rights or safety being respected.

For example, if you're crossing a border into a country or region where you think your device or data might be subject to search or seizure, when you're traveling alone in an area where you think you might be accosted, or when you're going to fall asleep with people you don't entirely trust.

In other words, if you think there's a chance someone will try to put your finger on the Touch ID sensor without your permission and approval or force you to unlock your iPhone X with your face, hit the kill switch and remove that possibility.

Any Touch ID or Face ID questions?

If you have any questions about Touch ID or Face ID, drop them in the comments below!

Updated December 21, 2017: Added steps for using Siri to temporarily disable Touch ID or Face ID.