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The buttons on Zenith’s original “clicker” remote were a mechanical marvel
(www.theverge.com)
This is a most excellent place for technology news and articles.
How I hate those "new" web pages spending 8 pages on fluff before even explaining how it works.
Thank you Google algorithm (it detects how long time you spend on a page after a search).
So after scrolling up, down left and right, I didn't find it (guess it's sound?).
Interesting. The link jumps straight to the article for me. No guessing involved. Yes, it's mechanically produced ultrasonic tones.