You open an EMF meter app, the needle settles, and the screen shows something like 48 µT. Is that high? Low? Something to worry about? Most people have never had a reason to think about magnetic field strength before, so a normal EMF reading is hard to judge without a reference point.
This guide explains what the number means, what you can expect in an ordinary room and what makes it move.
What your iPhone is actually measuring
Every iPhone has a magnetometer, the sensor that powers the compass app. It measures the strength and direction of the magnetic field around the phone.
An EMF meter app reads that sensor and shows the result. In Ghost Hunt, the EMF meter reads the magnetometer live and shows the change in microtesla (µT) on a needle gauge and a five-level LED bar.
It is worth being precise about what this is. Dedicated EMF meters used by electricians often measure electric and magnetic fields from wiring and appliances, sometimes at specific frequencies. An iPhone magnetometer measures the static and slowly changing magnetic field around the phone. It is a real measurement, but a different one.
The unit: microtesla
The tesla is the standard unit of magnetic field strength. One tesla is a very strong field; an MRI scanner uses one to three. A microtesla is one millionth of a tesla.
The Earth's own magnetic field, the one that makes a compass point north, is roughly 25 to 65 microtesla at the surface, depending on where you are. It is weaker near the equator and stronger near the poles.
That gives you the most useful reference point of all.
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What a normal reading looks like
In a typical room, away from electronics and metal, an iPhone magnetometer will usually show a total field somewhere in that 25 to 65 µT range. That is just the Earth's field, plus a little from the building.
You will notice the reading changes as you turn the phone or walk around. That is normal. The sensor picks up direction as well as strength, and buildings contain steel, wiring and appliances that bend the local field slightly.
Ghost Hunt adds a calibration step to make this easier to read. One tap sets your room's baseline, and from then on the meter shows the change from that baseline rather than the raw total. That way a calm room reads close to zero change, and anything that moves the reading stands out.
Always calibrate before you start
Hold the phone where you plan to begin, keep it still and tap calibrate. The meter will then show how far the reading has moved from that baseline. Re-calibrate whenever you move to a new room, because each room has its own background level.
What makes the reading jump
A sudden rise is exciting during a ghost hunt, but it almost always has an ordinary cause. Common ones include:
- Magnets. Fridge magnets, magnetic catches on cupboards, speakers and headphones all have strong permanent magnets.
- MagSafe cases and accessories. A MagSafe case, wallet or charger sits right next to the sensor and shifts the reading significantly.
- Electronics. Laptops, televisions, game consoles and chargers can all affect the field close to them.
- Metal. Steel beams, radiators, metal furniture and even a set of keys can bend the local field.
- Moving the phone. Turning the phone quickly changes the direction the sensor reads, which can move the number.
Ghost Hunt shows honest hints about these causes alongside the meter, so you can check the obvious explanations first.
Is a high reading dangerous?
The fields you will see on a phone magnetometer at home are small. They are in the same range as the Earth's own field, or a little above it near magnets and electronics. A phone sensor is not designed to assess health risks, and the readings in an app are for curiosity and fun, not safety.
If you have a genuine concern about electrical equipment or wiring in your home, ask a qualified electrician.
Using readings in a ghost hunt
For a fun investigation, the meter works best as part of a game. Calibrate in each room, walk slowly, and when the reading jumps, stop and look for the cause together. Is there a speaker behind the sofa? A radiator? Someone's phone case? Write down each cause you find, so the next time that room spikes you already know where to look.
In Ghost Hunt, real magnetic spikes are logged automatically during an investigation, kept separate from the Spirit Box's generated words. At the end you get a report card to share. Finding the ordinary explanation for a spike is half the fun.
Quick answers
What is a normal EMF reading in microtesla?
In most rooms, an iPhone magnetometer reads roughly 25 to 65 µT, which is about the strength of the Earth's magnetic field.
Why does my EMF reading change when I turn my phone?
The magnetometer measures direction as well as strength, so turning the phone changes the reading. Keep the phone still for a steady number.
Can an iPhone EMF meter detect ghosts?
No. It measures magnetic fields. Rises in the reading come from magnets, metal and electronics, not from spirits.
Why is my reading much higher than normal?
Check for a MagSafe case, magnets, nearby electronics or metal. Remove the case, move away and re-calibrate.
Where to get it
Ghost Hunt pairs a real magnetometer EMF meter with a generated Spirit Box for fun, with no microphone, no camera and no account needed. Download Ghost Hunt on the App Store for iPhone.
Calibrate, walk slowly and see what the room is really made of.