A few years ago, my employer was considering issuing smartphones (iPhones anyway) to people who actually do stuff. You know, they wear overalls and carry toolkits, spades, paintbrushes etc. I tried out one such device. I walked about half a mile through a building and then another half mile outdoors.
The tracking device Felt that, in my leisurely 10 minutes, I had been from southern England to the middle of the Bay of Biscay, back to the "Midlands", then to 0°N 0°E (somewhere south of Nigeria) and back to where I genuinely finished. They are not very accurate indoors! Do these secret bases not have a bit of shielding. If I was in the US military in Afghanistan, or the Russian one in Syria, I would be very keen that my facilities were proof against incoming mortars and snipers in the hills and trees outside.
If you are running round the perimeter track though, then you will draw a very neat line right round your base.