An ever-increasing feature of public spaces is the installation of security screening devices. Two types are common. There is the frame machine that you walk through, and there is the hand held wand, which the security person buzzes all over your body and in the case of overzealous ones touch and prod you as well.
For women unfortunate enough to carry a handbag, which is almost all women, they are subject to further indignity as the scanner is held over their open handbags.
The idea is to detect and locate undesirable objects that are hidden on a person's body. Both these types of scanners work using the principle of electromagnetic interference where the detector produces a tiny electrical current and therefore a magnetic field. Any metallic object conducts electricity and interferes with the magnetic field signalled by an alarm signal either an audible sound, a flashing light or both.
Metal detectors are old technology. In medicine, Alexander Graham Bell, inventor of the telephone, was asked in 1881 to use a metal detector to find an embedded bullet in the US President James Garfield who had been shot.
He did not find it, possibly because it had gone in too deep. This is because electromagnetic waves of the kind generated by such metal detectors do not penetrate very far. They can detect metal on the surface, something all of us are aware by the continuous buzzing at all mall entrances but they work poorly as security devices when their limitations are not known.
A metal detector cannot distinguish between a metallic belt buckle, a knife and a gun. It is therefore almost useless when applied to a handbag, which is almost always made of some metal. Its proper use then depends not so much on its property to detect metal but on the knowledge and training of the user.
When a metal detector goes off, the person holding the detector needs to make a judgment call what to do next. Almost everyone walking on the planet has something metallic on their being. So very few people will not set off a metal detector unless they deliberately prepare not to do so. So every minute of the day for the security person the metal detector signals something.
How do they know that this is something serious? Their judgment will depend on whether they use as their main principle customer convenience or security. If the principle followed is customer convenience then they let people through despite the buzzing noises because stopping every other customer for further security check annoys people and wastes time and would require more security personnel. If the perspective is security then the added cost is factored in and the burden is pushed to the customer to ‘pass the security test’.
Either which way, the problem is how to deal with the continuous detection of ‘nothing’.
In medicine this is the problem of ‘false positive’ where a laboratory test is done and the result says there is disease but really it is not there. There is the flip side, where a false negative occurs and the test does not pick up that a disease is present.
False positives occur when the barrier set to detect something is set very low so that it picks up many things other than what you really want and a false negative when the barrier is set so high that some of what you are looking for passes undetected.
Not all tests are 100 per cent accurate and so it is important to see a doctor first before doing any kind of test so that the right test can be selected and the results of the test, no matter how obvious be interpreted correctly. In the case of our public space the barrier is set very low so that there is continuous noise that something has been detected.
The result is that unless personnel are very well trained most of it is nuisance value because even when something is present likely the person has ‘buzz’ fatigue, while allowing some familiar people to pass through security check negates the entire purpose of the exercise.
There is a further fear that people have and that is being subjected to metal detectors can cause ill health. The electromagnetic dose that people receive is very low, for example, using a hair dryer emits more electromagnetic waves. However pregnant women and those people with heart pacemakers should not subjected to such devices.
There is one potential useful outcome of all these people being given basic training on metal detectors. A not uncommon problem that doctors face is a child who has swallowed a coin.
The terrified child is usually too distressed to say what they have done until much later. If you suspect your child has been pilfering your coins, walk to nearest mall and have a check.