How do modern metal detectors not detect cell phones, watches, etc. but still detect weapons?

Question

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

Answer 1

Phones and watches (and coins and car keys and …) are made with metal, but not as much metal in as solid a chunk as a firearm or hunting knife. The metal detector is tuned to ignore small amounts of metal but not large amounts.