Free · Android · GPS-based
An anchor alarm that actually wakes you
Set your swing radius, go to sleep. If the boat drags outside the circle, the screen turns full red and your phone plays a loud, continuous alarm — not a polite notification you sleep through. Free, GPS-based, works in anchorages with zero mobile signal.
Built for the 3 a.m. wind shift
Set the circle in seconds
Mark the anchor position, set the swing radius for your scope, done. Adjust any time without resetting the watch.
A real alarm sound
Drag outside the radius and the screen goes full red while the phone plays its actual alarm tone, continuously, until you respond — designed to cut through sleep, wind, and a buried phone.
Works with zero bars
Drag detection runs on GPS, which needs no mobile network. Remote bay, foreign cruising grounds, dead zone behind the headland — the watch keeps working.
Made for sleeping aboard
Set it and put the phone down. No babysitting the screen — the alert is loud enough to trust, so you actually rest.
Man overboard, one tap
The MOB button pins the exact position and shows live bearing and distance back to the spot until you clear it — on the same screen you already have open.
Free, with a real planner behind it
The alarm is part of Marine OS Navigator, the companion app to the Marine OS route planner — weather, fuel prices, and your planned routes all sign into one free account.
Set up in one minute
- 1Download the app and allow the install when Android asks.
- 2Sign in with a free Marine OS account (takes a minute to create).
- 3Anchor, open the Anchor tab, set your swing radius.
- 4Sleep. If the boat drags, you will know — loudly.
An anchoring aid, not a substitute for proper ground tackle, adequate scope, or prudent seamanship.
Frequently asked
Is the anchor alarm really free?
Yes. The anchor alarm, man-overboard button, live weather, and fuel prices in Marine OS Navigator work with any free Marine OS account. Route navigation of your saved routes is the part that belongs to Boater Pro.
How does the anchor alarm work?
Drop anchor, open the app, set your swing radius around the anchor position, and sleep. The app watches your GPS position; if the boat drifts outside the circle, the screen turns full red and the phone plays a loud, continuous alarm sound until you are back inside or dismiss it.
Does it work without mobile signal?
Yes — the alarm runs on GPS, which needs no mobile network. You can anchor in a remote bay with zero bars and the drag detection still works all night.
What radius should I set?
A common starting point: your scope (rode length) plus boat length, plus a margin of 10–15 meters for GPS wander. If the alarm triggers on a wind shift while the anchor holds, widen slightly; if you want earlier warning in a tight anchorage, tighten it.
Will it drain my battery overnight?
The app uses standard Android location updates rather than constant high-rate tracking. A typical phone loses a normal overnight percentage — plug in if you are below half charge at midnight, as you would with any anchor-watch app.
Is it available for iPhone?
The app currently ships for Android as a direct download. On other devices, the Marine OS web planner works in the browser, and the roadmap is driven by member requests.
Comparing options? Read our honest roundup of the best anchor alarm apps, or see everything the Navigator app does.