This is interesting now as it's a hot topic in the UK. The government claims this technology will finally be in use next year [1]. Apparently, it can detect concealed knives (even under heavy clothing) from 6 metres away using ordinary cameras combined with "electromagnetic infrared waves and a unique computer algorithm" [2]. I imagine this could be used to detect other types of metal weapons used more prominently in other countries.
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[ 2.7 ms ] story [ 21.1 ms ] thread[1] https://www.bbc.co.uk/news/uk-68085532
[2] https://www.standard.co.uk/news/politics/knives-crackdown-zo...
Also, how common are false positives? Like cell phones, a bunch of keys, small spray with medicine, ...
https://www.semanticscholar.org/paper/Automatic-detection-of...
I imagine coupling this information with data from a small magnetometer might build a sharper composite image.