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There are many old (and maybe more recent) watches that use GPS to track speed, distance, etc. but do not charge any sort of periodic fee for this. Is there any way to locate these using GPS if they are lost?

If not, is there any way to "hack" such a device so that it can be located using GPS if it is lost?

Example of such a watch: https://assets.timex.com/user_guides/W281_M434/W281_GPS_Marathon_QSG_NAEU_hires.pdf

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The Global Positioning System is a passive system which calculates the position by comparing tiny differences in the time, which is encoded into the signals, received from different satellites.

  • Nothing is transmitted to any satellite

  • A GPS device is not in itself "tracked" by any external device

The only way the position can be known externally is if there a network connection, and the Timex watch linked does not have one. It is possible that a 'smart' watch can be tracked, but not this one.

There is also a possibility that the location history can be obtained from the USB port, but of course you would need to be with the watch.

Anyway, the manual says about the battery life

A full charge will give 8 hours of GPS use.

so there will be a limited window of opportunity to locate it.

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  • Thanks! That makes sense. It sounds to me from what you're saying that the watch may know where it is, but the GPS satellites do not have any concept of where the watch is. – capet Mar 29 '20 at 3:15
  • @capet Exactly. Hollywood routinely gets this wrong--you can't track a GPS receiver except possibly by leakage of the intermediate frequency of the receiver and that's going to be incredibly weak given the power level a GPS receiver operates at. (Real world examples of detecting the intermediate frequency: TV detectors and radar detector detectors.) – Loren Pechtel Mar 29 '20 at 5:49
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    @capet that is right. The GPS satellites' job is simple: they broadcast a coded time signal based on a very accurate clock – that's it. It's a dumb broadcast so they don't know if any device is listening, let alone this one, like your local radio station doesn't know if you are listening. The watch does not have a transmitter. It uses fancy math and trigonometry, based on the different length of time it takes the signals to arrive from the satellites in view, to calculate its position. – Weather Vane Mar 29 '20 at 10:35

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