A TRACK message only conveys location. It doesn't mean I'm ok. If TRACK messages show no movement for a day then I'm probably dead.
An OK message means just that. If I'm overdue, but I send an OK message, it means "relax, don't worry, I'm OK" - even if it means I'm spending the night in the woods.
A CUSTOM message will tell you why I'm overdue - I decided to extend my trip by another day, or I got an Elk down, etc.
A HELP message means that my vehicle is stuck, broke down, out of gas, vandalized, etc. The right thing to do is contact the Sheriff dept for that county or State Police.
It is NOT an emergency.An SOS message is an emergency. The right thing to do is to communicate trip information, number of people in party, etc. to the SPOT GEOS Rescue Center. The GEOS Rescue Center will call those on the emergency contact list. If you are called, provide simple confirmation information like "yes, he is backpacking in Idaho, or no he's not in the Bahamas". The GEOS Rescue people are trained professionals who are trying to determine if this a real emergency or a false alarm. They will contact Search And Rescue appropriate for the area I'm in. Remember, the GEOS Rescue Center has the same message information with location coordinates that you do.
Overdue - I said I would be back on a particular day and I'm not. If I send OK messages and/or CUSTOM message, it means that I'm going to be late, but I'm fine. If I don't send OK/CUSTOM messages then something is wrong and it is probably a good idea to start contacting the Sheriff dept or State Police. It is possible that the SPOT messenger is broken, but it is unlikely that it is both broken and I'm overdue. 24 hrs overdue and no message is reason to contact the authorities who can activate Search And Rescue. It is extremely important that you give the authorities the message coordinates, so they know where to begin their search. Also, give them my intended destination. Be patient and make sure that they understand the latitude and longitude coordinates exactly as you see them. Make sure they understand that the coordinates are WGS84 format. Give them, via email or verbally this webpage so they can see the messages themselves. The following is a conversion utility if you need to convert from WGS84 to degrees,minutes,seconds http://www.fcc.gov/mb/audio/bickel/DDDMMSS-decimal.html .
In the example on the side, the latitude is 45.5191 and the longitude is -122.9455 (the minus sign is important)
Don't panic - I send the OK/CUSTOM messages for your peace of mind. I leave the TRACK feature enabled so that you can follow my adventure. If I need help I'll let you know.
SOS message followed by an OK message - It means that there is an emergency, but I'm relatively OK.
SOS message followed by 3 sucessive OK messages within 1 hr OR a CANCEL - It means that there is no longer an emergency. All is well. Tell the SAR folks that they can chill. I don't know whether or not you can get SAR to stand down once they've activated, but at least you should feel better.
No track or OK messages for multiple hours - if I'm not overdue, then SPOT may be broken. Normally I will send OK messages morning, noon and night.
Track messages keep coming, but my location doesn't change. After 24 hours of receiving messages like that it is likely something is wrong. I may have lost the SPOT unit. Or I may be dead in the trail.