Unlock Apple Watch
Unlock Apple Watch with iPhone
You can unlock Apple Watch whenever you unlock your iPhone.
Open the Settings app
on your Apple Watch.Tap Passcode, then turn on Unlock with iPhone.
You can also open the Apple Watch app on your iPhone, tap My Watch, tap Passcode, then turn on Unlock with iPhone.
Your iPhone must be within normal Bluetooth range (about 33 feet or 10 meters) of your Apple Watch to unlock it.
Tip: Your Apple Watch passcode can be different from your iPhone passcode—in fact, it’s better to use different passcodes.
Change your passcode
You can change the passcode you created when you first set up your Apple Watch by following these steps:
Open the Settings app
on your Apple Watch.Tap Passcode, then tap Change Passcode and follow the onscreen prompts.
You can also open the Apple Watch app on your iPhone, tap My Watch, tap Passcode, then tap Change Passcode and follow the onscreen prompts.
Tip: To use a passcode longer than four digits, open the Apple Watch app on your iPhone, tap My Watch, tap Passcode, then turn off Simple Passcode.
Turn off the passcode
Open the Settings app
on your Apple Watch.Tap Passcode, then tap Turn Passcode Off.
You can also open the Apple Watch app on your iPhone, tap My Watch, tap Passcode, then tap Turn Passcode Off.
Note: If you disable your passcode, you can’t use Apple Pay on your Apple Watch.
Lock automatically
Turn on wrist detection to lock your watch automatically when you’re not wearing it.
Open the Apple Watch app on your iPhone.
Tap My Watch, tap Passcode, then turn on Wrist Detection.
If you turn off Wrist Detection, you can’t use Apple Pay on your Apple Watch (1st generation) and Apple Watch Series 4 won’t automatically make an emergency call after you have a hard impact fall.
Lock manually
Touch and hold the bottom of the screen, swipe up to open Control Center, then tap 
.
Note: To manually lock your Apple Watch, you need to have wrist detection turned off. (Open the Apple Watch app on your iPhone, tap My Watch, tap Passcode, then turn off Wrist Detection.)
You need to enter your passcode the next time you try to use your Apple Watch.
You can also lock your screen to avoid accidental taps during a workout. While using the Workout app 
on your Apple Watch, just swipe right, then tap Lock. When you start a swimming workout with Apple Watch Series 2 and later, your Apple Watch automatically locks the screen with Water Lock.
If you forget your password
If you forget your password, you must erase your Apple Watch. You can do so in these ways:
Unpair your Apple Watch from your iPhone to erase your Apple Watch settings and passcode, then pair again.
Reset your Apple Watch and pair it again with your iPhone.
For more information, see If you forget your Apple Watch passcode.
Erase Apple Watch after 10 unlock attempts
To protect your information if your watch is lost or stolen, you can set Apple Watch to erase its data after 10 attempts to unlock it using the wrong password.
Open the Apple Watch app on your iPhone.
Tap My Watch, tap Passcode, then turn on Erase Data.
If you have a Mac running macOS Sierra or later, you can unlock your computer with your Apple Watch.