GhostScope How to use your iPhone as an EMF meter
Yes, an iPhone can detect one kind of EMF: its built-in magnetometer, the compass sensor, measures magnetic field strength in microtesla (µT). Open GhostScope, tap EMF Meter, then Start Hunt, hold still, tap Calibrate, and move the phone toward what you want to check.
Can an iPhone detect EMF?
Partly. Every iPhone has a magnetometer so the Compass and Maps know which way you face. It measures the magnetic part of the electromagnetic field, in three directions, and an app can turn that into a single strength number.
It does not see electric fields, Wi-Fi, cell signals or other radio waves, and it is too slow to read the 50 or 60 Hz alternating field around mains wiring the way a handheld EMF meter does. Think of it as a magnet and steel detector with a number on it.
GhostScope reads that sensor 20 times a second and shows the strength of the field as a big number, a ring gauge and a 5-LED bar. Pointing the phone at a strong source such as a speaker magnet should make the number climb smoothly rather than jump, which is a sign the meter is reading something real. If a device has no magnetometer, the app says so instead of inventing a figure.
How to take an EMF reading with GhostScope
- Take the phone out of any case with magnets and remove MagSafe accessories; they add a large, constant field.
- Open GhostScope and tap the EMF Meter tile (subtitle Magnetic anomalies).
- Tap Start Hunt. The reading starts, and the button turns into End & Save Session.
- Hold the phone still, away from electronics, for a couple of seconds, then tap Calibrate. The current field becomes zero and PEAK resets.
- Move the phone slowly toward the object you want to check: a speaker, a fridge magnet, a laptop, a wall socket.
- Watch the number, the LED bar and LEVEL. Tap Mark if you want the moment written into the hunt.
- When you are done, tap End & Save Session to keep the hunt in the Hunt Log, or just leave if you do not need it.
Why calibrate the magnetometer first?
Without calibration the meter never reads zero, because the Earth's own magnetic field is always there, usually a few tens of µT. On a typical phone that alone lights two or three LEDs.
Calibrate takes the current raw reading as the new zero. From then on the meter shows only how much the field has risen above that point, never a negative number. Recalibrate whenever you move to a new room, and always with the phone held still: calibrating while you swing it gives you a wrong zero.
This is different from the figure-eight calibration iOS sometimes asks for in the Compass app. That fixes the sensor itself; GhostScope's button just sets your starting point.
Worked example: a speaker on a desk
You calibrate in the middle of a room where the raw reading is 48.3 µT, then bring the phone close to a desktop speaker, where the raw reading climbs to 131.7 µT. GhostScope subtracts the zero point and multiplies by the sensitivity boost you chose in Settings.
| Situation | Shown | In mG | LEVEL | EMF Spike logged? |
|---|---|---|---|---|
| Calibrated, boost ×1.0 | 83.4 µT | 834.0 mG | 4/5 | Yes |
| Calibrated, boost ×1.4 (free maximum) | 116.8 µT | 1167.6 mG | 4/5 | Yes |
| Calibrated, boost ×2.0 (Pro) | 166.8 µT | 1668.0 mG | 5/5, gauge full | Yes |
| Back at the spot where you calibrated | 0.0 µT | 0.0 mG | 0/5 | No |
| Not calibrated, room only, boost ×1.0 | 48.3 µT | 483.0 mG | 2/5 | No |
At ×1.0 the ring gauge, which is full at 150 µT, is about 56% filled. The EMF Spike entry in the hunt records 83 µT, rounded, next to the note Auto-detected. Most people should leave the boost at ×1.0 for a first pass through a room; cranking it to ×2.0 straight away just makes a boring radiator look dramatic.
How to read the LED bar
The five LEDs go green, green, yellow, orange, red. They always follow the calibrated and boosted value in µT, even when you display mG.
| Reading | LEVEL |
|---|---|
| under 10 µT | 0 |
| 10 to under 25 µT | 1 |
| 25 to under 50 µT | 2 |
| 50 to under 80 µT | 3 |
| 80 to under 120 µT | 4 |
| 120 µT or more | 5 |
Common mistakes
- Reading without calibrating, then being surprised the meter never drops below two LEDs.
- Turning the phone around: that alone changes how the sensor sits in the Earth's field. Keep the same orientation and move it in a straight line.
- Leaving a magnetic case or wallet on the phone.
- Expecting the same numbers as a handheld EMF meter, which sees a different part of the field.
- Tapping Stop on the home card and expecting the hunt in the log.
Questions and answers
Does the iPhone have a built-in EMF detector?
Where is the magnetometer in an iPhone?
Should I use µT or mG?
Why does the number change when I just rotate the phone?
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- What is a normal EMF reading on a phone, and what causes spikes? · GhostScope
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