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by yholio
2776 days ago
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The headphone was a very small analogue receiver that had it's own micro-battery, an inductor and amplifier - all about 4mm wide and 8mm long. You would place it deep inside the ear channel and it was invisible even to a person standing right next to you. The signal was induced by a coil you would wear around you neck and you would pipe raw audio into it. Similar systems are even now on sale: https://www.olx.ro/oferta/sistem-de-copiat-casca-invizibila-... |
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