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I was expecting to be dissapointed (I thought this was going to be a test in the same room, with perfectly calibrated equipment) but I was wrong. Very impressive that you can do this at that distance and with affordable ($400) equipment. I wonder how long intelligence agencies have been using this capability.

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I knew someone who started building one of the laser based units in the fall of 1990, in high school. So that's 17 or 18?

By the end of the decade or beginning of the next, we had telecom hardware companies filtering the signal to the activity LED so that you couldn't read packet info out of the flickering.

Odds are good that someone combined those ideas a lot earlier than we might like to think.

I believe since the 80's

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