Erase Data on Watch

We all know of the great security features offered on an iPhone. I am curious if donating an Apple Watch, what options are available to make sure data has been overwritten. Does an Apple Watch have a function to wipe the free space, or its entire memory? Considering how much data an Apple Watch has, such as heart function, contact list, text messages, etc, I would presume security doesn't stop with the iPhone.

If anyone has any articles about how the security features, please let me know.

Best to everyone here

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