I discovered the purpose of what looked like an NFC tag in my toothbrush heads. More expensive smart versions of my toothbrush log how many times the head is used, and start nagging about replacement after a while. Unlike with printer ink, it at least doesn't disable old toothbrush heads.
https://hackaday.com/2023/05/27/hacking-a-smart-electric-toothbrush-to-reset-its-usage-counter/
How is this powering that LED? I mean, from the pictures in the hackaday article, it looks like there’s a metal ring in the base as one point of contact, and the motor head on the handle forms the other. But this is on when it’s not attached, which means there must be a small battery or super-capacitor in there too. That will then just get thrown away!
I’d really love to see a teardown of one of these if anyone knows of one? Or if you’re up for doing it once it actually needs replacing Bezier.
It's just a rewritable NFC tag in the head. The nagging happens via a mobile app the brush connects to.
I took one head apart out of curiosity when I first got this thing, and it's not much. But here's the insides of my current head anyway. Not like my dumb toothbrush needs it.
The aluminium ring is just for weight, or support.