An anchor alarm watches your position while you sleep and wakes you if the boat drags outside a safe circle. It is the cheapest insurance in boating, and your phone can do it. This guide compares the best anchor alarm apps in 2026, explains how drag detection actually works, and covers the setup details that decide whether the alarm fires in time or cries wolf all night.
For context: we build Marine OS, and our Marine OS Navigator app now includes a native anchor alarm - so we have a horse in this race. The apps below are still compared honestly, including where each one beats ours.
- An anchor alarm is a GPS circle: set the drop point and a radius, and the app alerts when the boat leaves it.
- Marine OS Navigator is our pick for a phone at the helm: full-screen red alert, the phone's real alarm sound, and the screen stays awake - in the same app that navigates your planned routes.
- Aqua Map AnchorLink is the most capable for multi-device setups: it mirrors the alarm across devices and sends remote alerts.
- Savvy Navvy and OpenCPN both include anchor watch alongside their navigation features.
- Set the radius from your scope plus GPS error, and mark the anchor at the moment you drop it.
- Phone-based alarms need power and signal to be useful all night, so plug the phone in.
#How an anchor alarm actually works
Every anchor alarm does the same thing: it records where the anchor went down, draws a circle around that point, and compares your live GPS position against the circle. If the boat crosses the line, it alarms. The quality differences are in the details: whether you can set the anchor position at the bow rather than where the phone sits, how it handles GPS jitter, whether the alert can reach a second device, and what happens when the phone locks.
#Marine OS Navigator - our pick
Marine OS Navigator is our Android companion app for the Marine OS route planner, and its anchor alarm was designed around one scenario: a phone at the helm or on the chart table, plugged in, watching the hook all night. Set the swing radius (15 to 150 meters), tap "Set anchor here & watch," and the app checks your GPS position every five seconds. If you drift outside the circle, the entire screen turns red with a DRAGGING ANCHOR warning and the phone plays its actual alarm ringtone on loop - the sound built to wake you - until you are back inside the circle or stand down. The screen stays awake automatically the whole time you are on watch.
What makes it our pick is what surrounds the alarm: the same app signs into your route planner account, navigates your planned routes with voice guidance, has a man-overboard button, and shows wind and wave conditions at your position - so the anchor alarm is one tab of the tool you already have open on board. Like every phone alarm, it wants the phone plugged in overnight. Download Marine OS Navigator - it works with a Marine OS account.
#Aqua Map (AnchorLink)
Aqua Map has the most complete implementation. AnchorLink mirrors the anchor watch across your devices, so the alarm set on the phone in the cockpit can wake the tablet in your bunk, and it supports remote notifications when you are off the boat. If you anchor out regularly, this feature alone can justify the subscription.
#Savvy Navvy
Savvy Navvy includes an anchor alarm with customizable parameters inside its navigation app. It is convenient if you already use it for routing, though it is a paid app and the alarm is one feature among many rather than the specialty.
#OpenCPN anchor watch
OpenCPN is free, open-source chartplotter software with a built-in anchor watch. It runs on a laptop at the nav station, which actually helps here: laptops have bigger batteries and do not lock their screens the way phones do. The trade-off is setup effort and having a laptop aboard.
#Dedicated anchor alarm apps
Single-purpose apps such as Anchor Pro exist for one job and do it with deep settings: swing zones instead of plain circles, GPS averaging, loud custom alarm sounds, and battery-friendly modes. If you anchor out most nights, a dedicated app plus a navigation app is a sensible combination.
#Browser-based anchor watch
The Marine OS route planner includes an anchor watch in its Underway mode: set the alarm at your current position with a 10 to 300 meter radius, and the chart shows the watch circle, your drift distance, and sounds an alert with vibration if you leave it. It runs in the browser on any phone with nothing to install. The honest limitation: a browser alarm works while the tab is open and the screen is on, so it suits an anchor check with the phone plugged in, not a locked phone in a drawer. Dedicated apps handle background alerts better.
If you let out 40 meters of rode in 5 meters of water, your bow can swing roughly 40 meters from the anchor, and the phone GPS adds 5 to 15 meters of error. A radius tighter than scope plus GPS error guarantees false alarms; much looser and you drag a long way before it fires. Mark the anchor position at the moment you drop, then add margin.
Marine OS is marina management software with a route planner for boaters. The Marine OS Navigator app carries a native anchor alarm (full-screen alert, real alarm sound, screen kept awake) plus route navigation, MOB, weather, and fuel prices - and the browser planner keeps a lighter anchor watch in Underway mode. Plan the passage, and the same account watches the hook at the end of it.
#Anchor tonight, plan tomorrow
An anchor alarm is one piece of the safety picture. Pair it with a float plan someone ashore can act on, and a tracking option so family can see where you are. For the planning side, see the best marine route planner apps.
A real anchor alarm, in the app that runs your routes
Marine OS Navigator: set the swing radius, sleep, and get a full-screen alarm with the phone's real alarm sound if you drag. Route navigation, MOB, weather, and fuel prices in the same app.
#Frequently asked questions
Frequently asked questions
Pick an alarm, learn its quirks on a calm night, and make it a habit every time the hook goes down. For the rest of the toolkit, see the best marine route planner apps and how to plan a boat route.
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