This is one about after flying rather than before flying, so please move it if it's in the wrong place

I have noticed recently that the Customs EU channels in UK airports (Luton for one) are being fitted with what appear to be scanner arches - a large metal arch around the bit you walk through, or sometimes two. Dover ferryport appears to have something similar that you drive through.

Does anyone know what these are and what they are for? I had a theory that they might be thermal imaging devices of some sort to detect stowaways and swine flu - or are they something else?

I'd have thought that if they were full-body X-ray machines there'd need to be some sort of notice for safety reasons?

Neil