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Perhaps you have encountered various watches and clocks that let you reset them (or they automatically reset themselves) to the Current Time as broadcast by some Official Govt Agency or other.
Imagine a watch that listens to that broadcast, and displays the time based on it alone? The broadcast consists
of one-beep-per second (the beep itself is likely a burst-of-data), so you know such a watch can display seconds the same as any other. Who needs a clock in such a watch!? It could be that such a radio-watch would consume less power than an ordinary watch (early "crystal radios" were entirely unpowered, except for the energy of the radio waves they absorbed).
OK, so I know that if you walked into a place where the radio broadcast couldn't reach, your watch wouldn't be able to display the time. How often does that happen for most people, such that WHEN inside such a place, they are there long enough that they need to know what time it is? Sure, some impatient types in an elevator car will not want this watch at all, but I never said it was for everyone, did I?
In case you want to set your clocks that don't have a radio time-watcher. [Vernon, Oct 14 2004]
Time Signal Formats
A whole bunch of different data formats, among them the beeps Vernon refers to. [jutta, Oct 14 2004]
Building a simple crystal radio.
"The reason a crystal radio does not need any batteries is the amazing capabilities of the human ear. The ear is extremely sensitive to very faint sounds." If I recall correctly, someone just found that donut-shaped molecule that's responsible for that sensitivity. [jutta, Oct 14 2004]
Lowest-power display I know of.
From their Web site, it could be that they have not thought about using their displays for watch faces. [Vernon, Oct 14 2004, last modified Sep 10 2010]
||Looks like the parts that your watch and the regular watches have in common - a display or hands or whatever - currently still consume enough energy to make being powered by radio waves unrealistic.
||[jutta], I'm not surprised. Perhaps this watch should require actually pushing a button to display the time. Or perhaps a lower-power display can be used (see qualcomm (formerly iridigm) link).