sweat with explosives. >> german officials say the scanners are too unreliable to use in their airports. here's abc's chief investigative correspondent brian ross. >> reporter: there are some 250 of the full-body scan machines in question. being used at 40 airports across the country. made by a u.s. company, l3 communications, they use radio frequencies to scan for hidden weapons and explplosives. at a cost of about $170,000 each, u.s. officials call them the best available technology. but that has now been challenged in germany where officials announced this week the machines and the software are currently too unreliable to be used. a ten-month trial at the hamburg airport found false alarms 49% of the time. often body sweat under the arms reading as explosives, according to german reports. it's a very nsitive device, said one police official. it picks up traces of everything on a person's body. the machines were already