Alarm not going off

Hello Wp10.

Thank you for using Apple Support Communities. Try restarting both your Apple Watch and iPhone to see if that helps: Restart your iPhone - Apple Support

If you're using an iPhone X, 11, 12, or 13:

1. Press and hold either volume button and the side button until the power off slider appears
2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.

Restart your Apple Watch - Apple Support

1. Press and hold the side button until you see the Power Off slider.
2. Drag the Power Off slider.
3. After your watch turns off, press and hold the side button again until you see the Apple logo.

If your Apple Watch is charging, take it off the charger first. When your watch is charging, you can't restart it. 

After your devices restart, delete the alarm that doesn't ring off of your device and re-create it: How to set and change alarms on your iPhone - Apple Support

• Swipe left over the alarm and tap Delete.
• Tap Edit, tap the Delete button , then tap Delete.
• Tap Edit, tap the alarm, then tap Delete Alarm.

Make sure all watchOS and iOS updates have been installed on your device as well:

Update your iPhone, iPad, or iPod touch - Apple Support

1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. If you see two software update options available, choose the one that you want to install.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.

Update your Apple Watch - Apple Support

1. Make sure that your Apple Watch is at least 50 percent charged
2. Connect your iPhone to Wi-Fi
3. Keep your iPhone next to your Apple Watch, so that they're in range
4. On your iPhone, open the Apple Watch app, then tap the My Watch tab. 
5. Tap General > Software Update.
6. Download the update. If asked for your iPhone passcode or Apple Watch passcode, enter it. 
7. Wait for the progress wheel to appear on your Apple Watch. It could take from several minutes to an hour for the update to complete. 

Leave your Apple Watch on its charger while the update completes. Don't restart your iPhone or Apple Watch, and don't quit the Apple Watch app. When the update completes, your Apple Watch restarts on its own.

If these steps don't work, you can try to unpair and re-pair your Apple Watch to your iPhone:

Unpair and erase your Apple Watch - Apple Support

Follow the steps listed under "How to unpair your Apple Watch from your iPhone".

1. Keep your Apple Watch and iPhone close together as you unpair them.
2. Open the Apple Watch app on your iPhone.
3. Go to the My Watch tab and tap All Watches.
4. Tap the info button  next to the watch that you want to unpair. 
5. Tap Unpair Apple Watch.
6. For GPS + Cellular models, choose to keep or remove your cellular plan. 

• If you want to pair your Apple Watch and iPhone again, keep your plan. 
• If you don't want to pair your Apple Watch and iPhone again, remove your plan. If you aren't going to pair with a different watch or iPhone, you might need to contact your carrier to cancel your cellular subscription. 

7. Tap again to confirm. You might need to enter your Apple ID password to disable Activation Lock. Before erasing all content and settings on your Apple Watch, your iPhone creates a new backup of your Apple Watch. You can use the backup to restore a new Apple Watch. After your Apple Watch unpairs, you'll see the Start Pairing message.

8. Set up your Apple Watch again.

We hope these steps help you. Cheers.