Open an EMF meter app on an iPhone and a number appears, usually in microtesla, usually moving. The obvious question is whether that number is real or decoration.
So can an iPhone measure EMF? Partly. In an app that reads the sensor the number is real, but narrower than most listings suggest. Your iPhone has no EMF sensor as such. It has a magnetometer, and what that part was built for sets the limits of the reading.
Can an iPhone measure EMF? The sensor you already have
Every iPhone since the 3GS carries a three-axis magnetometer, the part behind the Compass app and the beam in Maps that shows which way you are facing. It measures the magnetic field around the phone in three directions at once, which is how the phone finds north.
An EMF meter app adds no hardware; it reads that sensor and shows the field's strength instead of a direction. So yes, an iPhone can measure the magnetic field around it, within the limits of a part designed for navigation.
It is also why Compass can point the wrong way beside a speaker: the sensor adds Earth's field and any nearby magnet's field together.
What a microtesla reading means
The microtesla (µT) is a unit of magnetic flux density, the usual measure of how strong a magnetic field is. The useful reference point is Earth: at the surface its field is roughly 25 to 65 µT, weaker near the equator and stronger near the poles.
So the background is never zero, and steel in the building, radiators and appliances bend it from room to room. That is why a sensible app calibrates to the room and shows the change from that baseline. A raw figure in the forties tells you almost nothing; a rise of several microtesla near a shelf means something magnetic is on it.
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Free on the App Store for iPhone and iPad.
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What it can see, and what it cannot
The magnetometer is good at steady or slowly changing fields, which at home means magnets, and iron or steel. These reliably move the reading:
- MagSafe cases, wallets, chargers and magnetic car mounts
- speakers and headphones, which contain permanent magnets
- laptop lids, tablet covers and fridge magnets
- iron and most steel close to the phone (large steel objects further off too)
Copper, aluminium, gold and silver do not register, because unlike iron and most steels they are not ferromagnetic; many stainless steels barely register either. This is a magnetic field reading, not a metal reading.
Mains electricity is where people expect more than they get. Wiring and appliances produce alternating fields that cycle 50 or 60 times a second, and a phone magnetometer samples too slowly to follow them. Right beside a transformer or power adapter you may see some movement, but it is weak and uneven, and partly the steel and magnets inside the device.
Then there is what it cannot see at all: Wi-Fi, Bluetooth, mobile and 5G signals, and microwaves. These are radio frequencies, and the magnetometer is blind to them. It does not measure radiation of any kind.
How it differs from a K-II meter
The K-II, the handheld meter familiar from ghost-hunting television, works on a different principle. It shows field strength on a row of five LEDs set to milligauss (mG) thresholds and uses a single-axis coil that responds to alternating fields from mains wiring and appliances.
The units convert easily: 1 µT equals 10 mG. The measurements do not. A coil produces a signal only when the field through it changes, so a magnet held still beside a K-II gives it nothing to respond to, while the same magnet sends a phone's reading up. Beside an extension lead powering a heater, the reverse tends to happen: the K-II reacts and the phone's reading barely moves. A single-axis coil also has to face the field, so K-II readings change as you turn the meter.
Neither is the better meter; they answer different questions. The ghost hunting equipment guide covers the rest of the classic kit.
How accurate a phone reading is
Treat it as a rough indicator rather than a precise measurement. Accuracy and sensor position vary between iPhone models, so two phones in the same spot can show different numbers. The reading is also dominated by whatever magnetic or steel object is closest. A MagSafe case, a magnetic phone grip or a steel desk frame easily outweighs anything further away.
It is good at showing that something changed, and roughly by how much, and poor at absolute values comparable across devices.
It is also not a health or safety instrument, which is why this guide quotes no exposure limits. For health questions about power lines or appliances, ask your national health authority.
Getting a clean reading
- Take the case off if it is MagSafe, a wallet case or a folio with a magnetic clasp, and move magnetic chargers and mounts away.
- Clear a space away from steel desks, radiators, speakers and open laptops.
- Find your sensor. Slide a fridge magnet slowly around the edges of the phone and watch where the reading peaks. That is roughly where your model's magnetometer sits.
- Hold still and calibrate in the position you will use. In Ghost Hunt that is a single tap. Turning the phone afterwards can shift the number.
- Move slowly. Quick sweeps past furniture produce spikes that are only the phone passing steel.
- Repeat anything interesting, and recalibrate when you change room.
A spike nearly always has a cause
Most sudden jumps come from the phone passing something magnetic or steel: a radiator, a door hinge, a magnetic latch, another phone. Before reading anything into a spike, go back and see whether it repeats. If it does, the cause is usually close by, and finding it is the best part of the exercise.
Quick answers
Can my iPhone detect Wi-Fi or 5G radiation?
Not with an EMF app. Your iPhone's radios receive Wi-Fi and 5G in order to connect, but the magnetometer an EMF app reads cannot see radio frequencies, so a phone EMF app tells you nothing about a router or a phone mast.
What is a normal reading?
In absolute terms, around Earth's 25 to 65 µT. From a calibrated baseline, a quiet spot should sit close to zero with a little jitter; bigger jumps mean something magnetic or steel is near.
Why does the reading jump when I put my phone in its case?
MagSafe cases contain a ring of magnets, and wallet and folio cases often add more, pressed right against the back of the phone. Take the case off, or calibrate with it on and leave it on.
Is a phone EMF app good enough for a ghost hunt?
As entertainment, yes. It measures magnetic fields, not ghosts, and nothing it shows is evidence of anything paranormal. Whether spirit box apps work covers the other half of the usual kit.
Where to get it
Ghost Hunt: Spirit Box & EMF reads your iPhone's magnetometer live and shows the change in µT on a needle gauge and five-level LED bar, with one-tap calibration and beeps and haptics that speed up as the reading rises. Its Spirit Box is generated at random, for fun; nothing is picked up from the air. It is free with ads, with no microphone, camera or account.
Calibrate first, move slowly, and assume every spike has a cause you can find.