Compass anomalies — invisible layer

experiment 03 · magnetometer

the compass
knows what's hiding.

Walk slowly through a room while watching the compass heading. When you pass steel beams, rebar in the floor, electrical panels, or hidden pipes — the needle jumps. The magnetometer in your phone is sensitive enough to map the skeleton of a building just by walking through it.

the rebar grid inside every concrete building is magnetic. Construction companies use magnetometers to locate rebar and pipes before drilling. Security services use the same principle to map unknown buildings from the outside. Your phone does this passively — every compass app is already doing it.

—°

—

waiting

—heading °

—last jump °

0anomalies

distortion level

▶ how does this work?

Your phone contains a 3-axis magnetometer — the same sensor used by the compass app. It measures the total magnetic field in microtesla. Earth's field points toward magnetic north, but ferromagnetic materials (steel, iron, cast iron pipes) bend and amplify the field locally.

When you walk past a steel beam or an electrical panel, the heading changes suddenly — not because you turned, but because the local field is distorted. The jump in heading (in degrees) tells you how strong the anomaly is. A shift of more than 15° while standing still is significant.

The compass uses the deviceorientationabsolute event, which gives calibrated absolute heading in degrees from true north (0° = north, 90° = east, 180° = south).