Simpler solution which requires no input from those who dislike technology is a GPS tracker which installs in the OBD connector of any car built after 1997 or so. I installed one in a relative's car for about $250 and $16 a month subscription fee. I can access the car's position via a web site, even from my smartphone. While it won't call someone if the car is an accident like On-Star, you can set a geofence so you'll receive an alert via SMA or e-mail if the vehicle strays beyond a certain radius from a given spot. Other alert and alarm functions are available as well.

It uses 'cell' phone technology so it won't help if you're in the middle of telecommunications nowhere. I don't know if it would have helped this couple. They might have been out of range or didn't have anyone keeping track of them.

No connection, just a resaonably satisfied customer. See this site.