There is an app that already does this (among a few other emergency services related things) in the US - PulsePoint. I can sign up for nearby CPR needed alerts,

There is an app that already does this (among a few other emergency services related things) in the US - PulsePoint. I can sign up for nearby CPR needed alerts, and be shown on a map where AEDs are. I believe it was brought up when I took my last CPR certification 4 years ago, so it’s not exactly new.