Anchor Alarm App

This document was last updated on August 31, 2023.
The term "swing circle" (or variations of it) does not necessarily mean a circular circle, but means the area within which you are allowed to stay at anchor without sounding an alarm.

index of contents

Link to App Store

Exclusively in the App Store for iPhone, and iPad only. So head on over to the App Store! But if you want even more information feel free to read on here.


What is special about Anker Alarm?

Besides the tidy design, there are of course all the important features that are necessary for perfect operation. Here is an overview of the most important features that simplify your stay in the anchorage.

Not just circles

The special thing about this app is that you can draw your allowed swinging circle yourself, no matter if oval, triangle, or an L-shape. But if you don't like that, you can also set a circular swinging circle in the app.

Wake-up guarantee

The alarm sound will get you out of the bunk even after too many anchor beers, guaranteed!


The basic principle after opening the app is to draw in the swinging circle, and then arm the alarm. However, there are other options that allow you to draw or display, for example, the anchor with in the map to better estimate how you draw the allowed swinging circle.

The four tabs

Tab 1: Map

In the map you see a sketch of a small green ship, this is drawn to scale in the map. The corresponding dimensions can be set in the settings. The small green ship always points with the bow in the direction in which you hold your iPhone. Therefore, it is important for a correct representation on the map to hold the iPhone so that it points to the bow!
An orange line shows the distance covered. Thus, after a few hours of operation, you can see exactly where the ship has drifted. Thus you can see wind. You can reset this recorded track in the settings if necessary.
The rings show the distance (The distance at the circle is the radius) from you.
With the button draw swing arc you can either freehand or as a circle draw the allowed swinging circle into the map. Whether it is freehand or circle depends on what you have configured in the map handling settings.
With the set anchor position button you can draw the anchor into the map. You can set the anchor at most as far away from your position as it is possible with the water depth and chain length you set in the settings. A sketch above shows you during positioning how taut the anchor chain must currently be at the distance you have selected. This option is only available if you have activated the positioning of the anchor in the chart handling in the settings.

Tab 2: Help

Here is a guide on how to use the app.

Tab 3: Alarm

Here you can arm the alarm. There are two different alarms, the alarm based on the swing circle you allow. And the alarm that uses the device's internal compass to detect a course deviation if you have deployed bow and stern anchors and one of them is no longer holding, and the ship is turning. You have to activate the course alarm in the settings to see it here.
The swing arc alarm you can additionally mirror on a second device. So you can leave one iPhone or iPad (with cellular/GPS!) on the ship, and with the other on land always live check how the situation looks on the ship. The mirroring on another device you must first activate in the settings to see it here.

Tab 4: Settings

Ship dimensions
Your ship dimensions are taken into account and displayed to scale on the map.

Apple Watch

If you use an Aplpe Watch, you need to disable message mirroring for the Anchor Alarm app, otherwise the iPhone will not play an alarm but the watch will just tap once on your wrist which you probably wouldn't wake up from at night. You can find this setting in the Watch app on your iPhone here: Messages ➡ Mirror iPhone notifications from: ➡ Anchor alarm must be disabled!

Frame Color

When the app is on the screen can be displayed a colored frame, the color has a meaning in each case.


An alarm is armed, but the alarm is not triggered. So, depending on the alarm type, you are either inside the swing circle or course area you set.


An alarm has triggered. So depending on the alarm type, you are either outside of the swing circle or course area you set.


As with green, an alarm is armed, but in this case the device with the cyan frame is mirroring another device where the frame is currently green.


Why was there a new version?

I had to update the app because it no longer ran reliably on some devices, presumably because the code base was still developed for iOS 6 at the time and, from today's perspective, was based on many outdated architectural principles. This led to users complaining to me about crashes. Of course, this should not happen in an app that should be as reliable as possible! That's why everything is now new for the current state of the art.

I am missing the alarm when plugging in a headset from Verison 1

Most current devices do not even offer the possibility of headphones or a headset to plug in without a corresponding adapter, so I have not taken this type of alarm into the new version.

I miss the alarm at low volume from Verison 1

In version 1 the alarm was played in the currently set system volume. In version 2, a so-called "critical notification" is delivered by iOS. This is always in full volume, no matter if you have your iPhone turned down or even muted. Note that you must have allowed the app to deliver "critical notifications".

Are the measurements of the rings in the map radius or diameter

? It is the radius, and you (or your iPhone) are in the center, so something at the 25m circle is 25m away from you.

Planned Features

Imprint / Contact

Contact me please via this form.

Florian Kriesche
P.O. Box 190511
80605 Munich