The following can affect the water-resistance of your Apple Watch and should be avoided:

• Wearing Apple Watch in a steam room
• Wearing Apple Watch models other than Apple Watch Ultra or later in a sauna
• Wearing Apple Watch Ultra or later in a sauna above 55°C (130°F)

https://support.apple.com/en-gb/HT205000

Yeah ask your dad if he has a tag in the car and can share the tag with you and then it will show for you as the car and not alert you.

If he doesn’t then… you need to go around the car trying to connect to it unless it fell off the car already or they removed it already. I’m guessing outside the car if you had it locked. Under wheel arches and bumpers. Even if it doesn’t make a sound you should still be able to connect to it to locate it.