We're the developers of Family Tracker, just saw this thread, and would like explain a bit more in detail Family Tracker's GPS settings. We have 3 settings of operation for the background GPS tracking. In "Driving Only" mode we are actually not powering on the GPS, as the location is being retrieved via the cell towers. The location is updated only when there is a cell tower change (usually while driving). If you do not need super precise locations, we strongly recommend using this setting as it allows for huge battery savings, as the power used by Family Tracker is practically insignificant. As an example, beginning a 3-hour drive starting with the iPhone fully charged results in still having a 97% charge left after those 3 hours.
The "Always On" settings instead do keep the GPS radio in the device on at all times. This results in a better GPS accuracy, but will also result in a lower battery life (the charge won't likely won't last an entire day). With both the "Always On 1Km" and the 'Always On 100m" settings, Family Tracker will continue to update it's position even if the phone is stationary in one position (in 5 minute intervals). This will allow you to know that Family Tracker is still running on the phone and that the position being marked on the map is fresh and accurate. This is not possible to do in "Driving Only" mode.
Going back to the "Driving Only" mode, recently a new update (Family Tracker v2.1) became available in the App Store. With this update, when using "Driving Only" mode, we are briefly firing up the GPS for 20 seconds every time we detect the phone has stopped moving. This allows us to obtain a rather accurate position (often within 10-100 meters) as soon as the phone is still, while at the same time continue to maintain a very, very low battery consumption.
Finally please note that, when running in the foreground (i.e. left visible on the screen), Family Tracker runs the GPS in max-accuracy mode. This allows for real-time tracking if the phone is left on a car-charger for example (otherwise the battery drain will be very large). Do note that as soon as it's sent to the background, the above described GPS modes apply.
I hope this helps.
Roberto Franceschetti
LogSat Software