Only thing transmitted via Satellite on Onstar is the signal from the GPS satellites to the Onstar module. Voice communications are via digital verizon network, and one 6.1 version modules and older, there is an Analog backup via Verizon.
When you place a call on Onstar you go out via the little black antenna that is attached to the black wart on top of the H3. The wart contains the XM and the Onstar GPS antennas. (Wart is the engineering term for the three-phase antenna.
)
When you initiate a call to Onstar and ask for your location, the Onstar operator pings the Onstar module which has your location via the GPS system.
As for which is better. Lojack relies (or used to rely) on the local police having the equipment, which LoJack gave them to track. Smaller police departments did not have the equipment, so if the vehicle was stolen in the middle of nowhere (like Moab
), no way to locate the vehicle.
Onstar can locate almost anywhere there is voice communications via Verizon or one of their contracted service providers they offer for roaming.
If you are in a parking garage, you might be able to obtain cell service, but you will most likely lose GPS coverage. My Garmin, which is twice as sensitive as the GPS used in the vehicle, can't receive satellite coverage in a building with multiple floors or with metal/concrete ceiling, unless it is near a window or large opening. Near a large window or opening, the GPS might be able to get a signal from one or two satellites which will give your location pretty close.
Now, if Lojack has switched to GPS satellites, they will have the same limitations as Onstar.
Best feature of Onstar (versus first year free) is no special equipment is required by the Law, and the operators can track the police right to the vehicle. They also have a good reputation with the police. Onstar's range is only limited by the cell phone coverage, and with the older units (6.1 and older), with the capability of analog service, the coverage (until next year when analog goes completely away) is pretty darn good in the USA.