With satellite navigation, your navigational “landmarks” are space satellites whizzing through the sky above your head about 20,000km away, and because they’re constantly moving (not stationary, like Earth-bound landmarks), finding your position from them is a bit more tricky. A really good solution will rely on minimum of 6-7 satellites to get a good location, but 4 is minimum.
They key is that they are moving and the device you’re wearing needs to be able to “poll” to them to create the breadcrumb trail of your travels and find you if you’re in trouble. The GPS chipset in your device cannot reach the satellites through roofs and very dense forestry type foliage. If you’re always outside this is not a problem at all of course. If however, you might be inside when you get into trouble we would not find you, UNLESS your device was leaving a breadcrumb trail and we could see where you entered a building. Small devices that don’t have the battery life to support constant “polling” to the satellites, tend to send a test signal every few hours, or only when an alarm is activated. This means if an alarm is activated inside a building, we have no way of finding you.
So the work around is; use a lone worker monitoring device that is constantly sending location updates to the server, or there are solutions that can communicate to indoor locating beacons which is only good if you are always in the same building and very powerful if you need to locate someone fast within a multi storey/mutli room building.