Definitely worth wearing a medic alert bracelet or necklace. Since these are worn at your pulse points, they should be noticed by medics checking your pulse.
Also, it's a good idea to have an ICE (In Case of Emergency) number in your phone, ie next of kin etc. However, bear in mind that if your phone screen is locked, nobody can access your ICE no. - this happened to my Uncle, who had a heart attack at a bus stop in London. An ambulance was called, but despite him having his phone and numerous ID, no relatives were contacted for hours. The advice was to have your emergency contact no. on your phone's lock-screen. There is lots online about how to do this for different brands of smartphone.