Originally Posted by Oso Polar

Garmin navigators, at least some of them (e.g. my Edge Explore), do have incident detection. You can program a few phone numbers and in case device detects a crash, it'll send SMS texts to these numbers. I believe device detects crash by sudden deceleration - if it happens, it starts beeping and shows a countdown on the screen (1 minute AFAIR) during which you can cancel sending of the alert - if you'll not cancel it on time then it'll be sent. It happened to me twice (in more than a hundred rides, so this is not frequent) that Garmin thought the accident happened and started a countdown but these were just fast (real fast!) emergency stops from high speed. It'll not detect anything and not alert if you'll fall at low speed, at least this is my experience.