Does Touch ID work while you're asleep?
Touch ID reads a fingerprint, and Apple's Touch ID page doesn't describe a check that you're awake. What it does describe is when Touch ID stops and your password or passcode is needed instead: after a restart, after 48 hours without unlocking, and after five unrecognised attempts in a row. You can also switch fingerprint unlock off for the night.
Quick answer
Apple's Touch ID page describes how the sensor reads your fingerprint, and doesn't describe any check that you're awake. If that worries you, lock your Mac or iPhone and turn off Touch ID for unlocking before you sleep, or restart the device: Apple says your password or passcode is needed after a restart.
What does Touch ID actually read?
Your finger on the sensor. Apple says the sensor "uses advanced capacitive touch to take a high-resolution image from small sections of your fingerprint from the subepidermal layers of your skin". Touch ID then turns that into a mathematical representation and compares it with the fingerprints you've enrolled.
Apple puts the probability of a section of another fingerprint registering as a match at 1 in 50,000 with a single enrolled finger, and gives the odds of guessing a typical 4-digit passcode as 1 in 10,000.
Nothing in that description is about the person being awake. Apple's page doesn't describe a check that you're awake, so we don't claim one exists, and we don't claim Touch ID works on someone asleep either. What's certain is that it checks the finger, and that it stops working in the situations below.
Google says much the same about fingerprint unlock on Android: "A copy of your fingerprint could be used to unlock your phone." It adds that anyone whose fingerprints you add will be able to unlock your phone. Our guide on whether someone can unlock your phone while you sleep covers Face ID and Android face unlock.
When does Touch ID stop working and ask for your password?
Apple lists the times you must enter your passcode (iPhone and iPad) or password (Mac) instead of using your finger:
- After you've restarted your iPhone, iPad or Mac.
- When more than 48 hours have passed since the last time you unlocked your device.
- To add or delete a fingerprint.
- To change the passcode or Mac password, and for other security settings such as FileVault on a Mac.
- When there have been more than five unrecognised Touch ID authorisation attempts in a row.
- After you've logged out of your Mac.
On a Mac, Apple adds that you must have logged in already by entering your password before Touch ID can unlock it, and that you need to enter your password when you start up your Mac.
So the 48-hour rule doesn't help overnight. A restart does, and so does logging out on a Mac.
How do I stop Touch ID unlocking my Mac at night?
Two ways. Either switch off Touch ID for unlocking, or leave the Mac in a state where it needs your password.
Turn off "Use Touch ID to unlock your Mac"
- Choose Apple menu > System Settings, then click Touch ID & Password in the sidebar. You may need to scroll down.
- Turn off "Use Touch ID to unlock your Mac".
- Lock the screen: choose Apple menu > Lock Screen, or press Touch ID if your Mac or Magic Keyboard has it.
Turn it back on in the morning. Apple describes this option as allowing Touch ID to unlock your Mac with any fingerprint added to the current user account.
Or make the password necessary
Restart the Mac or log out before you go to bed. Apple says Touch ID can't be used after either until you've typed your password. More ways to lock are in how to lock your Mac screen.
How do I stop Touch ID unlocking my iPhone at night?
On an iPhone with Touch ID, the settings are in one place.
- Go to Settings > Touch ID & Passcode.
- Under Use Touch ID For, turn off the option for unlocking your iPhone. Apple's guide says that to turn off Touch ID, you turn off one or more of these options.
- Lock the iPhone.
Or restart it. Apple says a restart means your passcode is needed before Touch ID works again.
Apple also says that if your device is lost or stolen, Lost Mode in Find My stops Touch ID being used to unlock it.
Can two people use Touch ID on one Mac?
Yes. Apple says Touch ID can be used by multiple users on a Mac. Each user account can have up to three enrolled fingerprints, and a total of five can be enrolled across the system.
Fingerprints belong to a user account. Apple says only logged-in users can access their own Touch ID information, and an administrator can't change another user's Touch ID settings or fingerprints. Only user accounts that have passwords can be unlocked with Touch ID; sharing-only users and guest users can't use it.
It's worth checking which fingers are on your own account: Apple menu > System Settings > Touch ID & Password. To delete one, click it, enter your password, click Unlock, then click Delete. The full steps are in how to set up Touch ID on a Mac.
Could someone have added their fingerprint to my account?
Apple says you must enter your passcode or password to add a fingerprint. If you find a fingerprint you don't recognise, delete it and change your password. On an iPhone, go to Settings > Touch ID & Passcode, tap the fingerprint, then tap Delete Fingerprint.
If you think someone has already been into your Mac, our guide on who unlocked my Mac covers what macOS records and what it doesn't.
Where Failshot fits
Touch ID and your password decide who gets into your Mac. Your password is the first layer. Failshot is the second.
- With Failshot on, it photographs whoever unlocks your Mac, with a fingerprint or a password, then, with Pro, records a 5-second video. Video can be switched off.
- Whoever unlocks sees Failshot's window saying the unlock was photographed. With the Mac's built-in camera, the green light comes on.
- The unlock log lists every unlock Failshot recorded while it was on, with the time and how each one ended: confirmed by you, not confirmed, or a wrong Failshot PIN. It's free.
- Switching it off, or quitting it from its menu, takes Touch ID or your Failshot PIN and answer, never your Mac password. A wrong Failshot PIN or answer takes another photo.
- With Pro, turn on alerts and Failshot emails you about an unlock you don't confirm as yours.
Failshot for Mac is out now as a download from failshot.app, for macOS 14 or later. Free to use. Pro adds video, email alerts and the encrypted vault. Try Failshot Pro free for 7 days. Your card is taken at sign-up and charged on day 8 unless you cancel.
More questions
Does Touch ID work after 48 hours?
No. Apple says you must enter your passcode or password when more than 48 hours have passed since the last time you unlocked your device. Once you've typed it, Touch ID works again.
Does fingerprint unlock work while you're sleeping?
Neither Apple's Touch ID page nor Google's fingerprint unlock page describes a check that you're awake. Google says a copy of your fingerprint could be used to unlock your phone. To be sure, turn fingerprint unlock off at night or restart the device.
Does Touch ID work after a restart?
No. Apple says your passcode or password is needed after you restart your iPhone, iPad or Mac, and on a Mac after you log out. Touch ID only works once you've entered it.
How many fingerprints can a Mac store?
Apple says each user account can have up to three enrolled fingerprints, and a total of five fingerprints can be enrolled across the Mac.
Does erasing a stolen Mac turn off Touch ID?
Yes. Apple says that if your Mac with Touch ID is lost or stolen, erasing it remotely also disables Touch ID.