https://www.forbes.com/sites/daveywinder/2019/12/24/got-an-apple-watch-5-how-to-secure-it-in-three-simple-steps/

Do you need to secure your Apple Watch? — Well, if you check the security vulnerability database at CVE Details, you will see plenty of problems that could specifically impact WatchOS. There are 473 vulnerabilities listed in total, ranging from the low severity to the critical. But don’t panic; if you sort the results by “number of exploits,” you’ll notice there have been precisely zero so far.

Apple Watch security tip number one: Set a long passcode
Apple Watch security tip number two: Get smart with more locking options
Apple Watch security tip number three: Lost Mode and Activation Lock

For more Apple security advice, read How To Secure Your iPhone: 12 Experts Reveal 26 Essential Security Tips.