[nobody31415926]

There are two types.

Backscatter x-rays which use a low dose (hopefully) of x-rays but instead of measuring those that go through you 9as in a medical x-ray for bones) they measure the x-rays reflected back by metal objects such as guns and knives.

These do give you a dose of x-rays, hopefully a properly installed, maintained and operated system will limit this to a safe dose.

The alternative are mm-wave radar (terahertz imaging) these use similar radio waves to a mobile phone (but at lower power) They measure the change in the radio signal returned from metal and fluids in your body. Since they work on the same technology as mobile phones (but even lower power) they are assumed to be safe(r)