Soon, Apple Watch alerts will be audible even when they are in silent mode :

Apple Watch
Apple Watch : Alarm notifications will soon be audible and tactile thanks to a new feature in watchOS 11.4.
Today saw the publication of watchOS 11.4 release candidate, which offers a sneak peek at some of the upcoming features for the Apple Watch. In addition to fixing a few bugs, the OS update also changes the Apple Watch’s Silent Mode so that alarms can be heard when everything else is turned off.
At the moment, the Apple Watch only uses haptic sensations to notify users when in Silent Mode. It lessens distractions, keeps alerts private, and stops the watch from making noise when it shouldn’t, such during a conference.
The new functionality is described as “an option to allow Sleep Wake Up alarm to break through Silent Mode” in the notes for the watchOS 11.4 release candidate. There will be a new option to “Break Through Silent Mode” for each individual alarm, including the one that is programmed to wake you up in the morning under the Apple Watch’s sleep settings. According to 9to5Mac, when an alarm goes off, both audio and haptic vibrations will play.
Even with the Apple Watch’s haptics set to Prominent, the greatest intensity, I still frequently find myself falling asleep through the vibrations of an alarm I’ve set, which seems paradoxical to Silent Mode. I simply don’t utilize my Apple Watch for any important alerts since I won’t turn off Silent Mode, but that might soon change.
Silence alerts and notifications on Apple Watch :
You can use the Watch’s Silent Mode, Theater Mode, Do Not Disturb, or Focus settings to block out alerts and notifications. An alert can also be momentarily muted by covering the screen.
Turn on Silent Mode :

To turn off all notifications, alarms, and sound effects, go to Silent Mode. Haptic alerts are still sent to you.
Note: Even in Silent Mode, timers and alarms continue to ring while the Watch is charging.
To access Control Center on theWatch, press the side button.
Press the button for Silent Mode.
The Silent Mode button is selected in the Control Center.
On your iPhone, you may also open the Apple Watch app, select My Watch, select Sounds & Haptics, and then select Silent Mode.
Turn on Silent Mode :

Theater Mode keeps the Apple Watch dark by preventing the display from turning on when you raise your wrist. You still receive haptic notifications while in Theater Mode, which also activates Silent Mode and disables your Walkie-Talkie status.
To access Control Center on the Apple Watch, press the side button.
Press the “Theatre Mode” button.
The Theater Mode status icon shows at the top of the screen when Theater Mode is enabled.
When the Apple Watch is in Theater Mode, you can turn it on by pressing the Digital Crown, pressing the side button, or tapping the screen.
Activate Focus or Do Not Disturb :
Take these actions to stop haptic and sound alerts:
To access Control Center on the Apple Watch, press the side button.
Select Do Not Disturb or a Focus after tapping the Do Not Disturb button.
Press “On” or select an endpoint, for “On for 1 hour” or “On until I leave.”
See Use Focus on Apple Watch to adjust your Focus settings.

To temporarily quiet an alarm, cover the screen.
You can rapidly silence your Watch by placing the palm of your hand on the screen for at least three seconds whenever you receive an alert, such as an incoming call or the expiration of a timer. To make sure mute is turned on, you will feel a tap.
Go to the Apple Watch’s Settings app and select Gestures to enable Cover to Mute.