[katieHaylor (OP)]

Jerome asks:

Is it possible to see through walls - with drones, or thermal imaging? Is there any way to discover if anyone is using these technologies to spy on you? Can you somehow see what they're seeing?

What do you think?

[evan_au]

The easiest way to see through walls is to look in the windows. If this bothers you, close the curtains.

Seeing through opaque walls or a roof made of wood, brick, stone, tiles, corrugated iron or drywall is impossible, because these scatter or reflect the light.

If you are prepared to stretch the definition of "see" a bit, radar and Terahertz waves are able to penetrate walls. But radar produces images that are too fuzzy to be useful. With present technology, Terahertz waves are very hard to produce and detect.

The wall insulation in my house has a thin film of aluminium foil, which reflects heat, radar and Terahertz waves.

If someone really wanted to spy on you, it would most likely be done by monitoring the camera and microphone on your smartphone or computer. If you have turned on voice recognition (Siri, Cortana, etc), then snatches of your speech are regularly transmitted to computer farms for analysis.

Do you think that someone is spying on you?
Frankly, most of us are too boring to be worth the effort.

[wolfekeeper]

In some cases you can see people through walls using microwave radar. I think some government agencies may use it in hostage situations to know where people are standing before going in, but I don't know for sure. But yeah, it depends what the walls are made of as to how well it works, and the images would be very low resolution.

[alancalverd]

Police and military like to drill a hole in the wall and insert an endoscope. Surprisingly effective and rarely detected.

[CliffordK]

Light comes in all wavelengths, from long radio waves to ultra short gamma rays. 

Different materials are transparent, translucent, or opaque to different wavelengths. 

What we consider visible light is only a very small fraction of the spectrum.  And something that is opaque to visible light may well be transparent to IR, or X-Rays (one of the reasons that X-Rays are often used for internal imaging). 

There are two forms of scanning technology.  Active vs Passive. 

Consider Active technology like using a spotlight at night.  If they can see you, then you can also see (detect) them.  However, for example, using active IR may require special equipment to detect.

Passive technology will use natural emissions.  For example, IR is often heat dependent, and one may "see" body heat.  If you are carrying a cell phone in your pocket, then it is quite possible that the location of that cell phone could be precisely determined via microwave emissions/sensors.

Observing someone simply using a passive sensor is much harder to do, as one has to actually see the sensor, which can be small, or perhaps detect a secondary broadcast from the sensor (radio?)

Medical X-Rays are a pass through technology.  Source on once side, and detector on the other side.  Similar devices can be effective, say at border security gates where one can have fixed emitters/sensors, but may not be practical for other operations.  However, I believe there are X-Ray reflection devices that have the source and sensors on the same side.

Of course, as above, any active scanning technology can be detected, if one knows the proper bandwidth to observe, and has the proper tools.

[rami999]

i don't think so