Every commercial airport in the United States has unique security requirements based on the following security parameters: size of the airport; number of commercial operators servicing the airport terminal; access to designated zones in the airport; passenger throughput; and insuring an adequate airport staff for optimal, secure operation. The biological and machine elements in the airport security system are symbiotic in nature, due to the reliance of each element on the other for insuring reliable operation. Having one without the other is completely unreasonable in terms of insuring a secure airport.
The operation of security screening equipment is leveraged to enhance the existing investigative skills of the screening staff. Drug- and bomb-sniffing canines are used for their keen sense of smell in examining suspicious items, as this sense alone is much more sensitive than that of humans. Electronic surveillance equipment supplements human surveillance throughout the airport. X-ray machines are used to see into passenger belongings to look for suspicious materials (sometimes in addition to a hand search through said belongings if a more thorough search is warranted), allowing the screener to peer into passenger belongings without introducing the threat of disturbance due to a blind search. Chemical sniffing machines detect the presence of chemicals typically used in explosives. Full body scanners examine passengers attempting to board commercial airliners for weapons and other suspicious items.
As none of these elements are 100 per cent reliable on their own, the combination of all working in concert with one another is a truly great method for insuring a multi-faceted and effective approach to airport security. The take away here is that these devices are useless without a trained security screener to interpret the results and apply the correct action – sometimes contrary to what the results of a security device describe due to misreading of the scanned item.