In the past year or so, every time I’ve gone through a metal detector at concerts/events, they always say you can bring phones and watches and stuff like that through the metal detector and it won’t set it off.
How can metal detectors not be set off by all the metals in these things?
Are phones and watches made out of different metals than the ones found in weapons?
In: 3
Metal detectors create a magnetic field. When you introduce metal into a magnetic field it disturbs the field (this is just a property that metal exhibits) and the machine is simultaneously detecting and reading the field. The amount of disturbance of the field depends on the amount of metal. So small amounts of metal change the field less than large amounts. The software can be set to only alert when a certain threshold of change on the field has been reached. This can be seen in a “treasure hunter” type of metal detector with the headphones that old people are walking around on the beach with trying to find lost rings. It’s chirps quietly over small stuff and loudly squeals over larger metal stuff. That’s just a speaker connected to the sensor’s signal and amplified. If you programmed it to only squawk at a certain threshold, you’d have the same thing as the concert’s metal detector.
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