When riding solo I ride carrying a MTN Gaurdian. Family at home can track you and there is also a panic button. You need cell phone reception for the tracking but at least it will narrow down the seach if needed.
I think the idea of a personal locator is an excellent one. To go with a full GPS communicator is terribly expensive, but one can use a GMS transmitter & GPS receiver combination which obviously if you are out of reach of cell tower will at least give the last few co-ordinates before you went out of range narrowing the search grid considerably.
2 options here:
OPTION 1. Here is a simple device that takes a 3g card and once an sms is sent to it re-sends gps co-ords.
Costs approx R1125-00

Specifications:
Main Function: Family GPS Tracker with Messaging
GSM Frequency Bands: 850/900/1800/1900 or 900/1800Mhz
GPS Sensitivity: -159dB
GPS Positional Accuracy: within 10m
Typical Active Battery Life: >48 hours
Start Up Times
- Hot Start: 45 seconds (avg)
- Warm Start: 30 seconds (avg)
Power Source: Li-ion Rechargeable Battery (800mAh)
Dimensions: 70mm x 43mm x 17mm (L x W x D)
Manufacturer Ref: BXRZG8UONLYF
Technical parameters:
Weight: 40g
Network: GSM / GPRS
Chip: SIRF3 chip
Vehicle charging voltage :12-24V input 5V output
Handheld Charger Voltage :110-220V input 5V output
Storage Temperature: -40 ° C to +85 ° C
Operating temperature: -20 ° C to +55 ° C
Humidity: 5% - 95% non-condensing
Full power can work 1-2 days.
Product Notes:
Also provides GPS speed data for object velocity.
Molded casing with integrated loop design for lanyard or keyring use.
Three color LEDs to indicate power, GSM, and GPS status.
SOS button to send SMS help message to paired cellphone number.
Back of unit has indented area where ID sticker can be placed - A FIRST ON THE MARKET.
Package Contents:
OPTION 2:
2. If you have a phone with GPS on it you can load depending on your phone, software that is GSM based & interrogates your cell built-in GPS for co-ordinates and then sends those co-ordinates back to the person who requested them via sms.
Jughead had it on his phone and when we went away into the great yonder, it gave the wives peace of mind to be able to send an sms and then pop the co-ords into Mapsource and locate us. This is obviously the cheaper alternate as you use existing equipment but it only works on phones with operating systems like Windows Mobile and would not work on proprietary opsys.
My 2 cents worth