The alleged attempt by a Nigerian man to blow up a US airliner on Christmas Day has prompted some airports around the world to introduce full-body scanners. Experts say such a scanner could have prevented the passenger from smuggling the explosive device onto the plane.The scanner uses radio waves to see through a person’s clothing, allowing airport staff to spot any hidden weapons or packages. The German government wants them to be allowed at the country's airports. But the decision is controversial, and has privacy campaigners on the warpath.