It's the new full body scanner they rolled out in the States and now use in a number of other countries. You stand there like a star fish and the machine takes a scan of you to check for concealed weapons etc. The manufacturers state that it uses a new "harmless" type of imaging technology, and apparently does not detail genitalia etc. The scanner sends the pic to a person who looks at it and okays you or not. The person who is looking at the image is not supposed to see you personally, or be able to save the image in any way (they should be in another room altogether). They're just supposed to push the button to say yay or nay.
It is not supposed to be compulsory - you can opt for a pat-down instead.
My own personal experience in Miami was that I refused to go through it because to me it is still relatively unproven technology. I got the third degree about how it's just like being near a microwave or carrying a cellphone on my hip all the time. To which I replied I try to do neither of those things. "Well, it's like getting an xray" she says. To which I replied I don't do those either unless they are medically necessary. She really did not want to take no for an answer even though I was polite but firm.
She got REALLY huffy and made me stand to the side of the queue and then called another female officer to pat me down - in front of the 100 or so people waiting to go through security. No screen, no privacy. Because DH had the kids with him, they did not make him go through it. My hubby noted afterwards though that the guy who was checking the images was sitting not 15 feet away.
They cannot legally make minor children go through it. I'm not exactly sure of the reasoning behind this, either because it's a health risk for them, or because it takes essentially naked (albeit blurry and cartoonish) pictures which makes it child pornography. Either way, that makes it unacceptable to me to go through it. I don't mind the pat down, but some common courtesy would go a long way. The way the TSA officer's behaved was surly and combative. And if I could have been bothered, I would have laid a complaint (I was tired, with two tired kids by then).
When I went to Aussie earlier this year they had them in Brisbane. However because I was with my DD, they did not ask me to go through it. I was 4 or 5 weeks pregnant at the time, so even if they had, I would have refused.
I understand the "protective" reasoning behind the scanners, but I personally find them intrusive and offensive. I would opt for a pat-down (even an undignified public spectacle) any day.