It fell out of the large pocket of my hunting vest. The clip on the back of the unit was a large flat one made to hold a wide belt and must have slipped off the thin fabric of the pocket. I had rain pants on over my jeans so my belt was covered. With it in the pocket I could look at and use it easily, but it slipped out. It was not tied by a lanyard. It will be from now on.
The hand/held unit of the Garmen Alpha System came with a two part, swiveling belt clip which I used at first, but it was made to hold a narrower belt than I use. Then once it was stressed too much and the parts separated and couldn't be put together again. I called Garmin and they sent me - free - a replacement for the original and another single piece clip that holds a wider belt. Whichever kind you use, always use the lanyard.
Diane