Two things to get a better understanding of how the gauss meter works: Hall effect and Lorentz force.
Gauss meter works making use of the Hall effect. The semiconductor of the Hall effect sensor is charged with current. The magnetic field will pull or push electrons in the semiconductor and then creating voltage differences. This voltage is proportional to the magnetic field strength.
The magnetic field has a direction (expressed in X, Y, and Z). If the magnetic field direction is perpendicular to the current flow of the sensor, it will attract or push electrons at the maximum level. Herewith you can measure the magnetic field properly and accurately.
What are the Sensors?
Unfortunately, the magnetic field is invisible, we don’t know the direction. Fortunately, there is a 3-axis Gauss meter that employs three sensors for three-axis direction. The reading of the three sensors is calculated using the root mean square. You can easily get the reading result with high confidence.
Simply, a Gauss meter can be a 3-axis sensor or a 1-axis sensor.
When we use the single-axis Gauss meter, you will pick the right reading if the instrument/sensor is perpendicular to the magnetic field direction. It will take the wrong reading if you put it slightly bend or parallel. You have to turn around the Gauss meter gradually until you get the peak reading. This way can take time and has a high possible error.
In comparison with the 3-axis sensor, no need to turn around. The three sensors measure for yourself. And then the microcontroller will calculate those data into ready-to-consume readout output. Therefore, most Gauss meters are digital. The display will show the reading in Tesla (International) or/and Gauss (imperial).
The Frequency Range Response Matters
The next thing how the Gauss meter works is frequency response. It will only measure the magnetic field from the frequency that the meter knows. If the Gauss meter is designed to measure the magnetic field from a frequency of 60Hz, then it will only measure the magnetic field from the power line, surely not measure the magnetic field from magnets or cell towers.
This principle equals to how the underground wire locator works. If the receiver of the locator is designed to receive a 33 kHz frequency, then you have to inject 33 kHz into the wire. Otherwise, your receiver will not pick anything.