Can Your Phone Be an EMF Meter? What a Magnetometer Measures
EMF meters are a staple of ghost hunting, and almost every phone contains a magnetic sensor. So can a phone replace a dedicated meter? Partly — and understanding which part is the difference between a useful reading and a meaningless one.
You can try everything described here with the free EMF Meter and the three-axis Ghost Com II.
What “EMF” actually means
EMF stands for electromagnetic field, which covers a very wide range of things: the static magnetic field of the Earth and of magnets, the 50 or 60 Hz fields around household wiring, and the radio-frequency radiation from Wi-Fi, mobile phones and broadcast towers. A single meter rarely measures all of them.
Popular ghost-hunting meters such as the K-II respond mainly to alternating fields from wiring and appliances. A phone’s sensor measures something different.
What your phone’s magnetometer measures
The magnetometer is the sensor behind your phone’s compass. It measures the magnetic field around the phone on three axes — across the screen, along it and through it — in microtesla (µT). The combined strength of the three is the total field.
Earth’s magnetic field is roughly 25 to 65 µT depending on where you are. Indoors, steel beams, wiring, speakers and electronics shift that by a few microtesla, and a magnet held close can push it far higher. That is the range a phone reacts to well.
What it cannot measure
- Radio-frequency radiation from Wi-Fi, Bluetooth and mobile networks — the phone’s antennas use that, but its magnetometer does not measure it.
- Electric fields, which dedicated meters measure separately from magnetic fields.
- Mains-frequency fields in detail. The sensor samples too slowly to resolve a 50 or 60 Hz field the way a K-II or a gaussmeter does.
Milligauss and microtesla
Ghost-hunting meters usually show milligauss (mG); phone sensors and scientific instruments use microtesla (µT). The conversion is simple: 1 µT = 10 mG. Earth’s field of about 50 µT is therefore about 500 mG.
Because Earth’s field is always present, an absolute number tells you little on its own. What matters is change from the ambient field, which is why a good meter app lets you zero it.
How to take readings with a phone
- Remove magnetic cases, mounts and wallets — they swamp the sensor.
- Hold the phone still in an ordinary part of the room, away from chargers and speakers, and zero the meter.
- Move slowly. Rotating the phone near metal changes the reading on its own, and fast sweeps produce spikes caused by the movement.
- Before an investigation, walk past known sources — a laptop charger, a speaker, a fridge door — so you know what an ordinary spike looks like on your phone.
- When you see a change, check for the usual causes: wiring in the wall, an appliance switching on, metal furniture, your own movement.
Phones, browsers and sensor access
Not every browser can read the magnetometer. On Android, Chrome gives the most direct access to the raw field, though some builds keep it behind a flag. iPhone Safari exposes a compass heading rather than field strength, so apps use changes in the heading as a proxy for disturbance. Most laptops and desktops have no magnetometer at all.
A trustworthy meter tells you which of these it is using. The EMF Meter and Ghost Com II both show their source, and run a clearly labelled simulation rather than inventing numbers when no sensor is available.
Three ways to read the same sensor
The EMF Meter is the simple handheld readout: one number in mG or µT, peak hold and a graph. Ghost Com II shows the raw X, Y and Z axes, the ambient baseline and the difference, alongside a field plot and session log. The Anomaly Scanner turns the same signal into Geiger-style clicks, which is easier to follow while you walk around.