In the landscape of vintage tech, some devices stand out not just for their function, but for their audacious engineering. The Casio TM-100, released in 1987, is one such marvel. On the surface, it appeared to be a straightforward digital timepiece. Look closer, however, and its true nature was revealed: this was a watch with a clandestine FM radio transmitter built-in.

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Engineering Ingenuity Worn on the Wrist
The TM-100's magic lay beneath its plastic casing. Flipping a small lever above the LCD display activated its secret function. Users would raise a telescopic antenna and speak or play music into an integrated microphone. Powered by a dedicated second battery (separate from the timekeeping battery), the watch would then broadcast the audio signal.

  • Tuning In: A tiny tuning knob allowed the user to calibrate the transmission frequency. It covered the Japanese FM band (76-90 MHz) and a portion of the US FM band (87.5-108 MHz), making it functional, albeit with limitations, in different regions.
  • Miniaturization Feat: Packing the necessary circuitry for FM transmission into a wristwatch form factor in 1987 was a significant achievement in embedded systems design, predating the widespread miniaturization of wireless communication tech we take for granted today.

A Rare Artifact of Analog-Digital Convergence
The TM-100 occupies a peculiar place in tech history. It was never widely advertised and remains a relatively uncommon collector's item. Crucially, Casio never incorporated this transmitter feature into any other watch model. While similar FM transmitter gadgets existed in Japan – the birthplace of karaoke – embedding one into a wristwatch was unique.

"To us, the TM-100 is partially shrouded in mystery... The transmitter feature was never included in any other model." - Pocket Calculator Show

Proof of Concept: Bridging Eras
Decades after its release, the TM-100's functionality remains demonstrable. Enthusiasts like akitaishi have showcased its capabilities in modern contexts, such as using the watch to transmit audio from an iPod to a classic 1980s boombox via FM radio. This tangible link between digital audio files, vintage wireless transmission, and analog amplification highlights the watch's enduring technical novelty.

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Legacy of the Unconventional
The Casio TM-100 (Module 661) stands as a fascinating footnote in the evolution of wearable technology. It represents a bold, unconventional experiment in convergence – blending timekeeping with personal audio broadcasting long before the concept became mainstream through Bluetooth and Wi-Fi. Its rarity and singular design make it a coveted piece for collectors and a testament to Casio's willingness to explore the boundaries of what a 'watch' could be. While it didn't spawn a product line, the TM-100 reminds us that innovation sometimes appears in the most unexpected packages, pushing miniaturized electronics into uncharted territory, one fleeting FM transmission at a time.

Source: Based on original reporting and imagery from Pocket Calculator Show.