Starting with iOS 12, you will always have to unlock your iPhone or iPad to connect a USB accessory. This is because of “USB Restricted Mode,” which protects your iPhone or iPad from hacking tools like GrayKey.
Why You’re Seeing This Message
You’re seeing this message because of “USB Restricted Mode,” a security feature Apple added in iOS 11.4.1 and improves on in iOS 12. It prevents any USB devices from establishing a data connection while your iPhone or iPad is locked. Devices connected to your Lightning port can still charge your iPhone or iPad—they just can’t do anything else until you unlock it.
This protection was added because hacking tools like GrayKey have been exploiting USB connections to crack the PIN protection on iPhones and iPads. While GrayKey has been used by police departments and other government agencies, it’s possible this same technique would allow criminals to bypass your PIN and gain access to your iPhone or iPad. This shouldn’t be possible.
To prevent this exploit, Apple now restricts USB devices from establishing any sort of data connection while your iPhone or iPad is unlocked. That’s the default setting, anyway—you can disable this security feature if it gets in your way, but we don’t recommend it. USB Restricted Mode prevents people from gaining access to your iPhone or iPad without permission.
When you connect a USB device to your iPhone or iPad while restricted mode is active, you’ll see a “USB Accessory” notification that says either “Unlock iPhone to use accessories” or “Unlock iPad to use accessories.”
iOS 12 Removes the One Hour Grace Period
Apple originally added this feature to iOS 11.4.1. However, in its original state, there was a one-hour grace period. Any USB device could establish a connection as long as you had unlocked your iPhone or iPad in the last hour. And, after a device was connected, the timer would be reset.
In other words, anyone who got their hands on your iPhone or iPad would just have to plug any old USB device into the Lightning port within one hour after you’d last used it to bypass this protection. Apple added the one hour grace period to make this protection less annoying, but attackers could exploit it.
Even on iOS 11.4.1, putting your iPhone into Emergency SOS mode immediately enables USB Restricted Mode without the one hour timer. This also disables Touch ID and Face ID until you unlock your phone with your PIN or passphrase.
In the iOS 12 beta, Apple appears to be removing this grace period. If your iPhone or iPad is locked and you connect a device, you will always be prompted to unlock it. If USB Restricted Mode is enabled, your iPhone or iPad is always protected.
How to Disable USB Restricted Mode
We don’t recommend disabling USB restricted mode. When connecting a USB accessory, just unlock your phone or tablet—it should be easy and quick with Touch ID or Face ID.
But, if this feature is really annoying you, you can turn it off. Perhaps you use a lot of USB accessories and you find it annoying to unlock your iPhone or iPad each time. It’s your decision.
To disable USB Restricted Mode and let USB accessories function even while your device is locked, head to Settings > Touch ID & Passcode (or Face ID & Passcode). Enter your PIN to continue.
In the “Allow Access When Locked” section, enable the “USB Accessories” option. With this option enabled, devices can connect to your iPhone or iPad while it’s locked.
Again, we don’t recommend enabling this feature. It’s there to protect your private data from hacking tools that are currently being used in the real world.