SARLOC was originally developed in 2009 by Russ Hore as a web application that allowed Search & Rescue (SAR) teams to locate you if you were unsure of your position. If you had a data signal, the SAR team could send you a message that allowed SARLOC to obtain your location and add it to the SAR teams mapping systems. Although it has been hugely successful, it does require a data signal to show you a location before it can be passed to the SAR teams.
The SARLOC App will show you a location even if you do not have a data signal. If you are in voice communication with the SAR team you can tell them your location. If they provide you with a SARKey to enter into the App, you can share your location with them directly to their mapping systems.
SARLOC is not a substitute for knowing how to navigate the outside world and it is essential that you learn proper navigation techniques before venturing into the wild.
SARLOC requires you to be in contact with a SAR team before you can share your location with them. Starting SARLOC will not automatically notify anybody you require assistance.