[dustfinger]

> Only a receiver with the right equipment can pick up the hidden message.

So all an eavesdropper has to do is setup the right equipment then? I guess it is only invisible until the technology becomes more widely available.

[Knork-and-Fife]

They also have to know where to look.

The big claim in general appears to be that the signal is not obvious because it averages out to normal background radiation noise. The article doesn't communicate this well though.

The bit that you quoted, I think that's just a random sentence that looks dumb out of context. I don't think it means anything special.

[behehebd]

As invisible as radio signals then.

[adrian_b]

In general, it is very easy to detect that radio signals are present.

A better comparison is with radio signals for which a method of spread-spectrum modulation has been used, chosen such as to have a bandwidth so wide that the averaged signal falls below the thermal noise level.

Such radio signals will also not be detectable without special detectors.

WiFi and Bluetooth use spread-spectrum modulation methods but they have relatively low bandwidths, so they can be easily distinguished from thermal noise. Much wider bandwidths are required to prevent detection.

[Hobadee]

Now now... Let's be fair...

Radio broadcasts to everyone.

Light you can block off to a single direction.

Oh wait, directional radio antennas exist. Nevermind, yes. Exactly like radio waves.

[TeMPOraL]

> Light you can block off in a single direction.

Sorta, kinda. You're really only just attenuating things a lot. It's tricky to actually block it off fully.

Same with radio waves, as light is literally the same phenomena as radio waves, it's just shaking faster.

[behehebd]

Almost like its all electromagnetic waves