Is there a medical alarm system where I can be several miles away from home (say in automobile) and it still works?

The only alarm that works within your car that I know of is GM's OnStar. No medical alarm that works in and around the home, will work in the car.

There are One Touch phones that claim to be the answer, but they are big and bulky, and they often times don't work. They have both cellular problems and 911 problems.

We bought one of the popular brands of one touch cell phone alarms to check it out. We sent 3 cancellation letters to them, 3 phone calls to them, and a cancellation of our credit card to stop them from charging.

Your best bet, is a medical alarm for in and around the home, and a cell phone to call 911 in the car.