We have two Garmins. Garmin A is a basic walker’s device called an “eTrex h” (the “h” is for high sensitivity). Garmin B is a nüvi something (and what’s that umlaut all about?) for our cars. A friend of mine has one of the earlier eTrex (no “h”) models which is quite prone to losing contact with the satellites when walking under any moderate tree canopy. Mine seems better so the “h” has apparently done some good. However, both GPS devices have trouble when I turn them on inside our house; they go into “acquiring satellites” mode and usually fail. The eTrex h even helpfully asks, “are you indoors?”
Now, the French are quite keen on building tunnels so that they can pile roads, particularly autoroutes, through mountains that have inconsiderately been thrown up by the forces of nature in the road engineers’ way. I appear to be able to drive through a 1km tunnel with hundreds of feet of rock above my head without the nüvi (what is that umlaut all about?) losing touch with the satellites; my track remains well plotted on the road.
If Garmin nüvi can’t see thrü (if you can’t beat ‘em, join ‘em) my skimpy roof tiles at home, how does it manage to see through a mountain?