How anti-theft tags work - magnetostriction
Why Hacker News recommends it
HN recommends it as an informative explanation of what those tags are, especially in threads about implants and RFID.
What it is
Applied Science explains how retail anti-theft tags work. A tiny magnetostrictive strip acts as a mechanical oscillator excited by a magnetic field, and magnetizing or demagnetizing it arms or disarms the tag.
Recommended by 1 HN commenters across 1 different months, 2017 to 2020.
What Hacker News said
Recommends wolfgang42 · 2017-07 · on “Why People with Brain Implants Are Afraid to Go Through Automatic Doors”
Right, which is precisely why automatic doors are completely irrelevant. On a related note, here's an interesting and informative video from Applied Science on how these tags work: [this video]
Cites sannee · 2018-11 · on “Alarm over talks to implant UK employees with microchips”
Are you sure these tags are RFID? I have only ever seen magnetostrictive tags [1] (but I don't buy expensive clothing...). [1] - [this video]
Cites aftbit · 2020-12 · on “ACE: Apple Type-C Port Controller Secrets”
Those RFID tags are pretty minimal though. Basically just a thin trace antenna and silicon die directly molded into plastic. [this video] I still agree that it's amazing that our society can make functional structures with feature sizes in the nm/µm ranges so cheaply that we can afford to throw them away.