I’m not an EMT personnel but I can say as a diabetic that having at least some form of medical alert identification can be a life saver. For some strange reason when someone passes out the first thing people think is that they have low blood sugar, which is remedied with glucose. Without something to identify that I’m a diabetic if I pass out because of high blood sugar and they shoot me up with MORE sugar than I’ll probably go into a coma.
Same thing with AIDs patients, they wear identification since their blood is considered “toxic”. So EMT’s would have to wear protective gear before they begin to attempt to help them because their blood is contaminated.
People with metallic parts inside their bodies wear bracelets because the AED/defib machine would interfere with the operation of the equipment and cause more harm than it would help. By metallic parts I mean like artificial hearts and the likes.
I was a Medic when I first joined the Army, that’s where I’m getting my information from. Ask away for more examples if needed, I don’t want to steal anyone’s idea by making a really long post :P