If you already have a chartplotter with an anchor-watch function, it's fair to ask why you'd buy a separate device. The plotter's GPS is excellent, after all. The answer comes down to three practical things that have nothing to do with positioning accuracy.
Where does the alarm actually sound?
This is the big one. A chartplotter's alarm sounds at the helm — up in the cockpit or at the nav station, behind a closed companionway, while you're asleep in the forward cabin. You can sleep straight through it. A dedicated device puts an 85–90 dB siren on your nightstand, where it will actually wake you. An alarm you can't hear is not protection.
Does it run on ship's power all night?
A chartplotter anchor watch means leaving the plotter — and often the whole instrument bus — powered on all night, drawing from your house bank. On a small boat or after a cloudy day on solar, that's a real cost. A dedicated device runs 72+ hours on its own internal battery, completely independent of ship's power.
How easy is it to actually use?
Chartplotter anchor-watch menus are notoriously fiddly — buried in submenus, different on every brand. A purpose-built device is one button: drop anchor, set radius, done. When you're tired and it's getting dark, that simplicity is what makes you actually use it every night instead of "just this once" skipping it.
When the chartplotter is enough
To be fair: if you're a light sleeper, your cabin is near the helm, you're plugged into shore power, and you know your plotter's menus cold — the chartplotter anchor watch is genuinely fine. The dedicated device wins for everyone else: deep sleepers, forward cabins, boats on battery, and anyone who wants the alarm where they sleep.
For the app side of the comparison, see why anchor alarm apps fail, and for the full picture read the complete guide to anchor alarms.
Want a ready-made answer? AnchorKnight is a dedicated GPS anchor alarm built around everything below — 1–2 m positioning, a 72-hour battery and an 85–90 dB cabin siren. See pricing & reserve yours →