Having seen this posted on the unconscious rider sticky I gave it a go.
http://www.roadid.com/eCrumbs
it’s on my s4 and I gave it a go today. It let’s you set your lock screen with your next of kin phone no and any other details.
The best bit is when you start the app it sends a text to your nominated phone number to let them know your out and about and they have live tracking ( unlike other apps the app does not have to be installed on both phones).
I used it today on a 12 mile ride with my wife keeping an eye and it’s very accurate. Best part was a hot cup of tea waiting as she saw I was 2 mins away from home .
Total data use was under 2 meg and with endmondo running it used 17% battery power with a phone call too.
Not affiliated with the company. It just might help one day