ProPublica: The US Transportation Security Administration has quietly begun removing its x-ray “backscatter” scanners from some airports. The machines are being replaced by millimeter-wave scanners, which use low-energy radio waves. The switch is intended to speed up security checkpoints because the new machines do not require staff to visually evaluate the scanners’ images. The x-ray scanners raised concerns over privacy and faced criticism concerning the radiation dose travelers were exposed to. Although there are no health concerns with the millimeter-wave scanners, which use cellphone-like signals, some tests have shown that they have higher false-positive detection rates.