How to Identify Magnet Poles with a Smartphone

12.8.2019

How can you identify a magnet’s poles using a phone?

Many smartphones contain a magnetometer that measures the direction and strength of a magnetic field. With a suitable app, you can therefore make an approximate distinction between a magnet’s north and south poles.

First, check that your phone actually has a magnetometer.
Use an app for measuring magnetic fields or polarity.
Bring the magnet closer slowly, always with the same face towards the phone.
Check the result by repeating the measurement after turning the magnet around.

What is a phone’s magnetometer?

A magnetometer is a sensor that measures magnetic fields along three axes: X, Y and Z. A phone uses it for its digital compass, for example, and to determine its orientation relative to the Earth’s magnetic field.

An app can display:

the magnetic field strength,
the field’s direction relative to the phone,
changes in readings when the magnet is turned,
an approximate distinction between the north and south poles.

Magnetic mobile phone holder attached to a car air vent

Example of an app displaying smartphone sensor readings

How to identify a magnet’s pole, step by step

Remove other magnets and larger steel objects from the surrounding area.
Launch an app for measuring magnetic fields or identifying polarity.
Calibrate the phone according to the app’s instructions.
Place the phone in a stable position.
Slowly bring one face of the magnet towards the location of the phone’s sensor.
Note the result and mark the magnet.
Turn the magnet around and repeat the measurement with the other face.

Do not place the magnet directly against the phone. Gradually bringing it closer from a short distance is usually enough to identify polarity.

Why is it not enough to look only at the X and Y signs?

The meaning of the individual axes depends on the phone’s orientation and how the particular app displays them. It is more reliable to use an app that directly identifies polarity and verify the result by turning the magnet around.

What can distort the measurement?

a magnetic phone holder or case,
the speaker and other internal device components,
a steel table or structure,
other nearby magnets,
inadequate sensor calibration,
a distance that is too short or too great,
changing the phone’s position during the measurement.

If the readings behave erratically, move the phone elsewhere, recalibrate it and repeat the measurement.

Can you identify a pole without a phone?

Yes. You can use, for example:

a compass,
a magnet with poles already marked,
a dedicated magnetic pole indicator,
an instrument designed to measure magnetic fields.

When using a compass, remember that the north end of the needle is attracted to the south pole of the magnet being tested.

How does a magnetic phone holder work?

A magnetic holder for a car contains a neodymium magnet. One part attaches to an air vent, while a thin metal plate is fixed to the phone or its case.

The holder is practical because:

the phone can be attached with one hand,
there is no need for mechanical jaws,
the phone can be removed quickly,
the holder takes up little space.

Safe use in a car

The holder must not obstruct the driver’s view.
The phone must not interfere with vehicle controls.
Do not place it in an airbag deployment area.
Before driving, check the stability of the holder and metal plate.
A heavy phone or strong vibrations may reduce the stability of the attachment.

Frequently asked questions

Does every phone have a magnetometer?

No. Sensor availability depends on the specific phone model.

How can I check whether my phone has a magnetometer?

Use an app that lists available sensors or consult the phone’s technical documentation.

Can X and Y readings always identify a pole?

No. The result depends on the device’s orientation and how the app displays the readings.

Can a magnet affect a phone’s compass?

Yes. A nearby magnet temporarily changes the measured magnetic field and can cause inaccurate compass readings.

Is a magnetic holder suitable for every phone?

This depends on the phone’s weight, the case used, the metal plate’s position and the stability of the air vent.

Summary

A smartphone with a magnetometer can be used to make an approximate distinction between a magnet’s poles. You need a suitable app, a stable phone position and repeated measurements of both faces of the magnet.

Do not rely on a universal combination of X and Y axis signs. The result depends on the device, app and orientation.

Mount your phone without complicated adjustments

A magnetic holder lets you quickly attach and remove your phone when safely parked.

View the magnetic holder