I have the Edge 520, and it has the incident detection turned on (on the Connect app). The way it works is with an accelerometer in the head unit. I saw DC Rainmaker test this when it first came out, by throwing his into a field (didn't work). I find when I am stopped I tend to nervously "bounce" my front tire, and that sets it off. Once (well twice in a row) at a rest stop at a century, my bike fell over and I had to explain why my jersey pocket was wailing loudly. I was very red faced.

If you dont cancel it, it will send a text message to your contact.
For tracking, my wife and I use Google maps, with location sharing so she can see where I am. Sometimes after a long ride I will cruise up to the house and she has the garage door open for me already. She was wondering where I was for so long, and she sees I am heading that way.
This of course only works where there is a cell signal, and DOES NOT work for cheating or lying husbands (or wives), but we have nothing to hide!