We don't know what you think you know Karl... you eating old carrot cake again?
Do a quick google and you will see it pop up in quite a few forums. I was surprised myself too. It is resistant, but Sena says not to wear it in showers.. just bathing.
The 10 is not technically waterproof either, just resistant. but not nearly as many people claiming issues and moaning online.
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from Sena tech support:
AG-Sena Tech Support, Jul 10, 11:23 AM:
20s are not water proof, just water resistance to differing inclements of weather, which is a subjective and case by case definition.
Use and exercise fair caution when riding with them. I'd suggest not riding with them in any type of showers.