We have to keep a computer on in order to use the chartplotter w/gps, therefore our anchor watch consists of:
1. taking bearings on fixed objects far and near (at least 3 bearings, in different directions at least covering a 90 degree arc hopefully more, on objects suitable varying distances away depending on the size of the anchorage and the swing we expect to have) and keeping track of those through the day or night. If the objects are too far away, it won't do you any good since you won't notice the change as you drag. Too close and you'll be frantic for no reason.
2. set the hi and low depth alarm for appropriate range.
3. turn on the "tracking" feature the little Maemo Mapper chart plotter (freeware) which resides on our Nokia N810 (an organizer similar to a Palm with features similar to an IPhone w/o the phone but with a gps). This is the "back up" chart plotter which takes no energy. No alarm on it, but you can see your track and know if you're still where you think you are.
When it's stormy, even if the computer and chart plotter are available, I must say I'm more comfortable if I'm taking bearings and keeping watch in that manner. I do like the idea of the range-finder from the golf store, too