You must be kidding!

I've lived at anchor most of the time for the last five years, often in
very deep water, and I get great peace of mind from the anchor watch on
my Furuno GP-31. I use the plotter function to see where I dropped the
anchor and then put set a go to cursor point there. The plotter draws
a nice swing arc or circle and the alarm tells me when I move outside
the circle... I dragged anchor three times in five years and the alarm
told me about it each time. Works great in anchorages up to 150' deep
with wind and tide -- been there. Maybe Garmin's function is different
from Furuno's...

-- Tom.