What this app does
Anchor Alarm watches your boat's GPS position while you're anchored. If your
boat drifts beyond the safe distance you set, it sounds a loud alarm so you can
react before you drag onto rocks, the shore, or another boat. It also warns you
if the GPS signal is lost.
Getting Started
- Allow location access. When the app asks for your
location, tap Allow. The app cannot work without GPS.
- Keep the app on screen. The app keeps your screen awake
while monitoring so the GPS stays active. If your phone warns that wake lock
isn't supported, set your screen to stay on.
- Choose your units. Pick Meters or
Feet at the top.
Setting Your Safe Distance
Use the Safety Radius slider to set how far the boat may move
from the anchor before the alarm goes off.
Tip: A good starting point is the length of
chain/rode you let out, plus your boat length, plus a margin for GPS error and
swing. Don't set it too tight or you'll get false alarms when the boat swings on
the wind.
GPS Accuracy Filter (optional)
The GPS Accuracy Threshold slider controls how strict the app
is about GPS quality. Readings worse than this value are ignored, so a single bad
fix won't move your anchor point or trigger a false alarm.
Tip: Leave it at the default (30 m) for most
situations. Lower it for very precise anchoring; raise it if you're in a spot with
weak signal and the app keeps rejecting readings.
Setting Your Anchor
- Drop your anchor and let the boat settle and pull back on the rode.
- When the boat is holding, tap SET ANCHOR.
- The app takes 10 GPS readings over 10 seconds to find an
accurate anchor point. Watch the progress bar and the "Good / Rejected"
counter.
- If signal is poor you can tap CANCEL and try again.
After capture you'll see a result:
- Anchor set ✅ – Confidence HIGH ⭐⭐⭐: Great fix, you're
good to go.
- Confidence GOOD ⭐⭐ / LOW ⭐: The anchor is set but
accuracy is lower. Consider re-setting with a clearer view of the sky, or use
a slightly larger safety radius.
- No reliable GPS — try again: All readings were too weak;
the anchor was NOT set. Move to a more open area or wait for a better signal,
then tap SET ANCHOR again.
Understanding the Display
While you're anchored, the status panel shows, in real time:
- Status – SAFE, checking drift, drag alert, or GPS issues.
- Distance from Anchor – how far you are from where you set
the anchor.
- GPS Accuracy – green = good, yellow = fair, red = poor.
- GPS – confirms the signal is live and how long since the
last update.
Alarms and Alerts
- DRAG ALERT! 🚨 means your boat has moved beyond the safe
radius for several readings in a row. Go check immediately. After you've
handled it, tap SILENCE ALARM.
- GPS FAILURE ⚠️ means the app hasn't received a GPS fix for
over 2 minutes and can no longer monitor your boat. Check your location
permission, signal, and that the screen is on, then tap
Acknowledge.
Best Practices
- Keep the device plugged in — continuous GPS drains the battery.
- Set the anchor after the boat has settled, not while still moving.
- Re-set the anchor if you re-anchor or let out more rode.
- Give yourself a sensible safety radius to allow for normal swing and GPS
error.
- Don't rely on the app alone — keep a normal anchor watch.
Troubleshooting
- "GPS ERROR" or no position: Make sure location permission
is granted and you have a clear view of the sky.
- App keeps rejecting readings: Raise the GPS Accuracy
Threshold or move to a more open area.
- Screen turns off: If wake lock isn't supported, set your
device to keep the screen on while anchored.
- When you leave: Tap RESET to clear the
anchor and stop monitoring before you get under way.
DISCLAIMER
Anchor Alarm is provided as a supplementary aid to assist with anchor watch and
is not a substitute for prudent seamanship, proper lookout, or approved marine
safety equipment. GPS accuracy, device battery, signal availability, operating
system behavior, and alarm reliability can vary and may fail without warning. You
remain fully responsible for the safety of your vessel, crew, and property at all
times. Use this app at your own risk; the developers accept no liability for any
loss or damage arising from its use.