This is a year old, but I only learned of it recently, and have heard that first responders’ awareness of this function is becoming known.
The Health app in iOS allows for you to define an emergency medical information page that is accessible on your device even if the screen is locked.
Caleb has his phone with him always. Caleb is not always compliant with wearing his medical ID. I find this feature very attractive.
I have it set up on my phone as well, including not only my personal medical information but also the fact that I have a 12 yo type 1 diabetic son.