Obtain internet connection

Why should we tell you how to sponge off someone elses internet?

The nerve of some people. Stanley, I suggest you get a job and pay for your own services.

(snip)

Do you mean to detect which frequency is being received?

The resonant circuit in the first stage of the tuner means it absorbs slightly more at that frequency than others, but that would be pretty hard to detect.

For many receivers, though, there is enough leakage from the local oscillator that one might detect it. This leakage is why radios and televisions receivers are not allowed on airplanes in flight, and also because the frequencies used for air traffic control aren't far from FM radio and TV frequencies.

The same would probably work for detecting receivers without detecting the frequency, though looking for roof antennae would be another way.

There are stories about US government being able to detect the RF emission from computer monitors and reconstruct the image on the screen. That is, for security reasons.

-- glen

This sounds more like wiretapping. There was a story once of someone who overheard her neighbor's drug deals through a cordless (not cellular) phone on her AM radio. The police came and recorded the conversation off the AM radio, and it held up in court.

It may or may not have if one used a scanner instead, but pretty much the law is that one should not expect privacy from a cordless phone.

There is a special US law regarding cell phones and their frequencies. The favorite example being the recording of Newt Gingrich on his cell phone.

(snip)

Well, encryption is different. Also, I am unsure about the ability to sell commercially equipment to receive signals that would otherwise require a license, and there is also the DMCA to worry about.

In general though, with specific exceptions, you are allowed to receive but not redistribute the information, especially if it could be considered unintentional. (Such as the AM radio case above.) That is, for personal use only. Of course if you don't tell anyone you are much less likely to get caught.

-- glen

AFAIK, they are detecting noise in the UHF-band from the antenna cable.

-Øystein

Yes. Or at least (for this purpose) to detect reception in a certain set of bands. Then you walk up and verify the presence of an apparatus capable of doing the stuff you're collecting the taxes for.

Something I found in a book full of anecdotes and stories, describes a slightly different way: one sends out so much that some (part of the) amplified reception circuit has to do something with the excess energy, and sends it out again. Like prodding in the dark until something goes ``eep''. NB, I'm not an EE, the details are hazy as I read that book ten years ago, and this all might be a quirk only found in equipment long gone, the stories were at least 20 years old back then. Hence the note that one'd want to ask someone knowledgeable, say a radio amateur. I just remember someone relating an instance where this trick did work.

For the purpose of weeding out where to look and where to skip, that'd be enough already. The point of the electronics is merely to make the check more efficient, not to make the checkers obsolete.

I've seen it demonstrated a couple of years ago, and it does work. But that demonstration also showed that the picture contains lots of noise. Then again, I've heard it was possible to reconstruct an image from the rather scattered image on the wall behind (well, in front of) the monitor, so the electromagnetic version of the reconstruction may have improved substantially too.

A simple access point does not do routing or NAT, it's closer in function to a switch or bridge.

Leaving an access point open would be pretty much the same as installing an Ethernet port on the outside wall of your building, and using an open access point without permission would be the same as plugging in to such a port, and using whatever you found you were able to connect to.