Security Review: Metal Detectors and Security Checkpoints

By Trip Volpe at 6:01 pm on February 3, 2008 | 2 Comments

Anybody who has flown on a national airline or had business in a federal, state, or county government building has certainly had the experience of waiting in the queue to be ushered through a beeping metal-detecting portal, separated from bags and other belongings which are whisked through an adjacent X-ray machine. Such devices are usually intended to secure the premises against an outside threat entering with weapons or other dangerous items.

Assets / Security Goals:

  • Physical safety of facilities beyond the checkpoints. Airplanes, for example, are very sensitive pieces of equipment, and hundreds of fatalities could result if they were tampered with or sabotaged with explosives. Additionally, transit hubs generally contain very dense crowds which could be vulnerable to attack.
  • Protection of infrastructure. Airports and airlines form a vital part of the travel infrastructure, and serious damage to the economy can result if that infrastructure is damaged or compromised.


  • Outside individuals who wish to enter the facility with weapons or explosives for the purpose of carrying out an attack, e.g. terrorists.
  • Insiders who might tamper with the equipment, either for the purpose of letting in outsiders, or to
  • Outsiders who wish to surreptitiously carry tools other than weapons into a facility for the purposes of extracting property or persons, e.g., a person smuggling a file into the county jail to help a prisoner escape.
  • Another potential “adversary” is simply a lazy or incompetent operator, who through inattention to the proper operation of the screening equipment compromises the security of the system.


  • Concealment of dangerous items in dense containers.
    X-ray and other screening devices rely upon the dense materials in knives, firearms, and other weapons to obstruct electromagnetic waves and thus give away their shape. If such an item were concealed in a small lead box, for example, the only outline visible would be that of the box, concealing the nature of the item inside.
  • Poor personnel training / lack of attentiveness.
    While the technology may be very adept at detecting metal implements concealed on a person or displaying the contents of luggage, such capabilities are not useful if the equipment operators are not sufficiently trained to recognize threats. For example, a recent tester was able to carry a fake bomb through airport security, a feat which many previous tests had also achieved.
  • Insufficient attention to perimeter security.
    Airports and other secured facilities usually have narrow points of ingress which are tightly controlled, but if there are other ways of approaching the premises that are not so closely guarded, the entire system is insecure. Anecdotally, I once visited a federal government building with extensive security checkpoints at all doors – however, when I was in the bathroom, I observed that there were wide, unlocked, and actually opened windows low to the ground and providing unrestricted access through an adjoining alleyway.


  • A careful security policy could help prevent persons from successfully concealing weapons inside opaque containers – simply require that large opaque objects detected in screening be separated and examined manually by screeners. Generally, this should not excessively difficult, as relatively few travelers carry large blocks of lead in their luggage.
  • One possible way to increase the effectiveness of screening hardware (against the inability of its operators to always identify threats) is through the use of software that uses image processing to attempt to automatically detect certain kinds of threats – for example, the outline of a knife, or characteristic elements of improvised explosives.
  • A source of shaky perimeter security is often the repurposing or augmentation of existing facilities for secure use – for example, many courthouses were built before such technology existed, and so their window and hallway layouts are not ideal for narrowing channels of entry. A response to this would be to construct new buildings when very high security is required. This is very expensive, but it allows facilities to be designed specifically to have all points of access restricted by screening equipment.

Risk Analysis:

When securing facilities such as courtrooms or other similar government buildings, the risks are often not sufficiently great to justify significant expenditure. Thus, the installation of screening equipment at entrances is usually considered secure enough for a courthouse, without barring all the windows (which would itself present a fire safety risk) or tearing down the building and constructing a new one. Facilities such as jails, however, do require more consideration, as a jail constructed by retrofitting an insecure building might fail to perform its intended function of securely containing its inmates.

It has been seen that the consequences of faulty airport security can be catastrophic, as when the attacks of September 11, 2001 claimed nearly 3000 lives. Therefore it seems reasonable to expect that significant efforts to improve security would be justified. However, there are trade-offs involved: as security screening processes become more invasive, the privacy of individual travelers becomes a concern. Some people may stop flying if the security measures become overly inconvenient, which creates a business pressure on the airlines. Further, some criticize many new security measures on the grounds that they provide little actual security, when much simpler measures (locking cockpit doors and arming the pilots) would be completely adequate to counter the threat (hijacking of airplanes).


If used properly, screening devices do provide considerable security against a threat entering an area with explosives or other weapons. However, this relies in great deal on careful security policy and proper training of operators. As we have seen in examples like that discussed in the linked news article, these things are often found to be lacking in the current arena of airport security. Although many enhancements to the technological capabilities of the devices are no doubt on the way, such advancements will not significantly improve security if they are not accompanied by an increased awareness of the human element. Additionally, it will be increasingly important to consider if improvements in security are necessary or even desirable as the cost to individual privacy and convenience increases.

Filed under: Physical Security,Policy,Privacy,Security Reviews2 Comments »


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    Comment by dschen

    February 3, 2008 @ 10:07 pm

    Regarding the detection of explosives, mass spectrometry has started to become popular. By bombarding a sample with a beam of ions, one can find the mass/charge ratio of all ions in the sample and eventually determine whether there are any hazardous substances inside. Mass spectrometry is also non-invasive, and just requires sticking on a special patch to a piece of luggage and placing the patch into the mass-spec. While this can detect very low amounts of explosives, mass-spectrometry is only used on a random sample as well as a selection of suspicious packages, as a result, only good training can put the sensitivity of the technology into use. However, if mass-spectrometry were to be used on all luggage and packages then the probability of explosives entering a secure area via the mass-spec would become near zero.

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    Comment by dubai

    February 6, 2008 @ 1:41 pm

    i had metal plates in my arm from an operation, that was fun and games trying to get through the security gates!

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