[hammock]

In the US, the backscatter x-ray machines are two giant ugly blue boxes that you stand between. The mm wave machines are more futuristic-looking, white cylinders that you stand inside of. (photos here http://www.flyertalk.com/forum/practical-travel-safety-issue...)

The technology deployment is airport-specific, so you will only find one or the other at any given airport, e.g. O'Hare uses Backscatter, Midway uses mm wave.

La Guardia is the one airport serving a major US city that does not have any of the new scanners, which can be nice if you typically opt-out.

[libraryatnight]

Thank you, this is very useful.