Gradiometer: Magnetic Detector

Turn your phone into a live magnetic field monitor.

Gradiometer reads your device's built-in magnetometer and shows you the magnetic field around you in real time - the total field strength, how fast it is changing, and how far it has drifted from the local background. When you sweep the phone past something magnetic, you see it immediately on the gauge and the live graph.

WHAT IT DOES

- Live field strength in microtesla (uT) or milligauss (mG), your choice
- Animated gauge that reacts instantly to changes in the field
- Anomaly score combining the deviation from the local baseline with the rate of change
- Rolling 60-second trend graph so you can see the shape of a disturbance, not just a number
- Adjustable sensitivity threshold with optional sound and vibration alerts
- Guided figure-8 calibration with a live sensor accuracy indicator
- Session recording with peak, average and duration, saved on your device
- CSV export of any session, so you can open your data in a spreadsheet
- Light, dark and system themes
- Designed for phones, tablets and foldables, in any orientation

BEING HONEST ABOUT WHAT A PHONE CAN DO

A true gradiometer uses two magnetometers separated in space. Your phone has one. So this app measures the magnetic field at a single point and derives its change over time and its deviation from a short rolling baseline. That is genuinely useful for finding disturbances, but it is not laboratory-grade spatial gradiometry, and we would rather tell you that up front than sell you a fantasy.

It responds to iron, steel, magnets and magnetic field disturbances. It will NOT find gold, silver, aluminium, copper or other non-magnetic metals. No app can, because those metals do not disturb a magnetic field in a way a magnetometer can see. Accuracy depends on your specific device's sensor, and readings are affected by nearby electronics, speakers, cases with magnets, and metal furniture.

WHO IT IS FOR

- Hobbyist prospectors and detectorists who want a quick pocket check
- Geocachers hunting magnetic caches
- Students and teachers exploring magnetism and Earth's field
- Electricians and DIYers locating rebar, studs with steel fasteners, pipes and wiring
- Anyone curious about the invisible magnetic landscape around them

PRIVACY

Your sensor readings never leave your device. Sessions are stored locally and are deleted when you delete them or uninstall the app. There are no accounts, no sign-in, no cloud sync, no location access and no storage permission - CSV export uses your system file picker. The app shows ads through Google AdMob, and consent is handled with Google's official consent flow before any ad is requested.

If your device does not have a magnetometer, the app will tell you clearly instead of showing you fake numbers.

Recent changes:
First release.

- Live magnetic field readings in microtesla or milligauss
- Anomaly detection using deviation from a rolling baseline plus rate of change
- 60-second trend graph
- Guided figure-8 calibration with a sensor accuracy indicator
- Session recording with CSV export
- Adjustable sensitivity, sound and vibration alerts, light and dark themes
- Tablet and foldable layouts