Magnetic Field & EMF Detector

The scan for what you cannot see at all

The lens scan needs a visible aperture. The infrared check needs an active illuminator. The wireless scans need a radio you can reach. Every one of those assumes some part of the device is exposed to you. The magnetic field detector makes no such assumption — it responds to the hardware itself, wherever it is.

Your iPhone contains a magnetometer, the same sensor the compass uses. It measures the local magnetic field continuously and precisely. Electronics distort that field: speakers and vibration motors contain permanent magnets, transformers and inductors concentrate flux, and current flowing through any circuit generates a field of its own. Hold the sensor close to a concealed device and the reading departs from the local baseline.

Baseline first, everything else second

A magnetometer reading is meaningless in isolation. Earth's field varies by location, and every building distorts it — steel framing, reinforced concrete, ductwork, radiators and wiring all shift the local value. A number that would be alarming in one room is ordinary in another.

So always start by establishing what normal looks like here. Stand in the middle of the room, away from walls and appliances, and watch the live graph settle. That value is your baseline. From then on you are not reading absolute numbers, you are reading deviations — a sharp rise as you approach a specific point, and a fall as you move away. A localised spike is a finding. A generally elevated room is a building.

How to sweep with it

1. Move slowly and stay close. Magnetic field strength falls off very steeply with distance, roughly with the cube of it for a small dipole source. Practically that means a few centimetres from the surface, not an arm's length. A sweep from across the room detects nothing.
2. Trace surfaces rather than waving. Run the top edge of the phone along the object — the length of a headboard, the frame of a mirror, the face of a smoke detector, the underside of a shelf, the trim around a vent.
3. Watch for a peak with edges. A concealed device gives a reading that rises to a maximum over one spot and drops off on both sides. That shape is what you are hunting, not a high number.
4. Confirm the peak from another approach direction. Come at the same point from a different angle and confirm the peak lands in the same place.
5. Explain it before you escalate. Then check that spot with the lens scan and, after dark, the infrared scan.

Everything that is not a spy camera

This is the mode with the most false positives, and being honest about that is what makes it usable. Screws, nails, hinges, brackets, door strike plates and picture hooks all read strongly. So do speakers, phone chargers, laptop power bricks, magnetic cabinet catches, mattress springs, floor heating, wall wiring, radiators, ducting and the steel in the wall itself. In a modern building you will find dozens of magnetic anomalies and none of them will be a camera.

The right way to use this mode is therefore second, not first. Do not sweep an entire room with it and try to explain every peak — you will be there all night. Use the other scans to build a shortlist of suspicious objects, then use the magnetometer to ask one narrow question about each: is there electronics inside this thing that should not have electronics inside it? A wooden picture frame that spikes hard has something in it. A bedside clock that spikes is a clock.

Used that way it is the scan that closes the gap the others leave open: devices sealed inside a fitting, behind a two-way mirror, or inside a wall, where there is no lens to see, no light to catch and no network to join.