An X-ray security scanner that can see through clothing was put into its first operational use Friday at Sky Harbor International Airport and could be rolled out to two other major airports by year's end.

The so-called "backscatter" technology has been controversial, with critics saying the high-resolution images are too invasive. But the Transportation Security Administration adjusted the machine's images so the normally graphic pictures can be blurred in certain areas while still being effective at detecting concealed weapons or other threats.

Passengers selected for secondary screening by the device are asked to stand in set spots in front of the closet-sized X-ray unit with hands palms out, then turn around for a second screening from the back. The entire operation takes about a minute.