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.
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.
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.
> 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.