Trackleaders PING app:

Trackleaders PING is a free app that sends tracking points when cell coverage is available. No SOS/911 function - dial 911 instead. Battery drain is minimal using the app, but phone must stay out of airplane mode.
More info on the app: Ping App
App instructions:
Search for "Trackleaders Ping" on the App Store / Google Play. Run the App. Enter your phone# (same phone# you just register with here). Start tracking. You should see yourself pop up on the map within a minute or two (once you are added to your desired map, which is a manual step). Let us know if you don't (info@trackleaders.com).
Fire up the app and turn tracking on at the start of your trip, and track when you want to.
Important: phone number entered here must match the phone number you enter in the 'Ping' phone app.