What about a device that knew everyone you knew? So when an ambulance went down...

What about a device that knew everyone you knew? So when an ambulance went down the street, a big sign on the roof could flash
DON'T WORRY! DON'T WORRY!
if the sick person's device didn't detect the device of someone he knew nearby. And if the device did detect the device of someone he knew, the ambulance could flash the name of the person in the ambulance, and either
IT'S NOTHING MAJOR! IT'S NOTHING MAJOR!
Or, if it was something major,
IT'S MAJOR! IT'S MAJOR!
And maybe you could rate the people you knew by how much you loved them, so if the person in the ambulance detected the device of the person he loved the most, or the person who loved him the most, and the person in the ambulance was really badly hurt, and might even die, the ambulance could flash
GOODBYE! I LOVE YOU! GOODBYE! I LOVE YOU!
One thing that's nice to think about is someone who was the first person on lot's of people's lists, so that when he was dying, and his ambulance went down the streets to the hospital, the whole time it would flash
GOODBYE! I LOVE YOU! GOODBYE! I LOVE YOU!