Turn On iMessage Contact Key Verification and Verify Your Contacts

This guide turns on Contact Key Verification, a setting most iPhone owners have never opened. Once it's on, iMessage can warn you if an unrecognised device turns up in a conversation, and you can compare a short code with the people you message most. You'll also check your own account for devices that shouldn't be there. Allow about 20 minutes, plus a few minutes for each contact you verify.

Why bother

iMessage is end-to-end encrypted, but your iPhone trusts Apple's key directory to say which devices belong to the person you're messaging. If an extra device's keys are slipped into that directory, it can quietly receive the conversation too. The encryption itself can't tell you, and Apple's usual new-sign-in notice wouldn't cover a tampered directory. Contact Key Verification adds automatic checks against a public log (Apple calls it Key Transparency) and shows an alert in the chat when something doesn't add up. Apple lists "a new, unrecognized device was added" to a contact's account as one of the causes of that alert. Comparing codes with a friend, once, gives you a checkmark that confirms you're talking only to their real devices.

Before you start

• Time: about 20 minutes for setup and the account check, then 2 to 3 minutes per contact.
• Devices: every Apple device signed in to iMessage with your Apple Account must run iOS 17.2 or later, iPadOS 17.2, macOS 14.2, watchOS 10.2 or visionOS 1.1. That includes an old iPad in a drawer or an Apple Watch.
• Account: the same Apple Account for iCloud and iMessage, two-factor authentication on, a passcode or password on every device, and iCloud Keychain turned on for all devices.
• Not supported: Managed Apple Accounts (the kind a school or employer issues).
• Your contacts: they need an iPhone, iPad or Mac with the feature turned on too, and they must be saved in your Contacts app. Android has no equivalent setting, because this only covers iMessage (blue bubbles).
• Checked on: Apple's current documentation for iOS 27 and macOS 27, which also covers iOS 26, macOS Tahoe 26, Sequoia 15 and Sonoma 14. The menu names are the same in all of them.

Steps

1 Update every device signed in to your account

1. On iPhone or iPad, open Settings > General > Software Update and install any update available.
2. On a Mac, open Apple menu > System Settings > General > Software Update.
3. On Apple Watch, open the Watch app on your iPhone and go to General > Software Update.

You should see that each device is up to date. If an old device can't reach iOS 17.2 or macOS 14.2, sign out of iMessage on it. On iOS 17 and earlier that's Settings > Messages > Send & Receive, tap your Apple Account, then Sign Out (on iOS 18 and later the same screen is under Settings > Apps > Messages).

2 Remove devices you don't recognise from your account

Do this before turning the feature on, so you start from a clean list.

1. Open Settings and tap your name at the top.
2. Scroll down to the list of devices. Tap anything you don't recognise or no longer own.
3. Tap Remove from Account and confirm.

On a Mac: System Settings, click your name, scroll to the devices, click one, then Remove from Account. On the web: sign in at account.apple.com, choose Devices, then click a device and Remove from Account.

You should see only devices you own and use. If a removed device comes back, it's still signed in somewhere. Change your password (see "If something goes wrong") so it gets signed out.