Lili, I agree with you - I never wear any jewellery, apart from a watch, so have never considered a medical alert item. Fortunately, my partner of over 10 years have never mentioned it - I think he knows I'd tell him not to be so daft. I only tell people who really need to know and who I can trust to keep quite about diagnosis, but then no-one has ever needed to do anything diabetes-related to me. When I was knocked off my bike by a driver who didn't look before opening his car door, I was able to tell the people who helped, bystanders, off-duty policewoman, ambulance staff, A&E etc, and didn't loose consciousness at any point.
But, if you do want to wear something, there are lots of options listed in these posts. Only thing I'd add is that unless it looks medical, emergency staff won't look for it / read details.