As David and magicman said in really thick tree canopies they can lose the satellites, but as you keep walking and get into thinner trees or a small opening they will pick the signals back up. I had to walk back up a large hill or small mountain(whatever[&:]) in the pitch black one night and though losing the signal a couple of times for just a few seconds it picked the signals back up and took me straight to my buds waiting on top as I followed the same path I took. I was over a mile from them and there were bears around! Between carrying my bow, GPS, radio, and flashlight I chose to turn the radio off and put it in my pocket. I would no doubt have passed my buds and our camp by over a half-mile without my Etrex.