Our editor is speaking with Dr Simon Goodyear, PhD, CEO Metrasens and his Chief of Security Products in a gloomy cell in a custody suite where they are both working. The company produce metal detectors of a special kind and they are here to evaluate the use of their product in such an environment. Metrasens developed the first commercially available ferromagnetic detection product in 2003. They are now the leading global supplier of such systems with sales, installation and service in three continents...

What is so special about your product, from a layman’s point of view. What do your Metrasens machines do?

How does it signal when it has detected something?
SG It has a row of lights that are activated when it detects metal. It is best used by the prisoner standing within a few feet and turning around. It will not work if a prisoner is having to be closely escorted by another officer as the machine will detect any metal the officer is carrying.

You haven’t mentioned any limitations have you?
SG It will not detect copper or aluminium, however most weapons, other dangerous and disallowed objects do have some ferrous content.

...and the range?
SG It depends on the object, it will detect a phone at one metre, smaller items need to be closer. There are ways of operating it which allows detection of small blades - in fact it has been demonstrated that our system will out-perform any other system on the market.

I’m thinking of a prison application. How might they be used with advantage?
SG Depends on the operational scenario. In a custody suite for example, the detainee would be taken to a wall mounted instrument and asked to rotate. The instruments have been deployed in a number of prisons in the UK and are used in several different modes.  Most useful, we believe, are free standing and randomly deployed. For example, when prisoners are about to leave a workshop, the knowledge that an instrument might be placed at the door might well deter the theft of a dangerous instrument.

I can also see an application during visiting times, detecting metal contraband in the possession of a visitor before a chance occurs to pass it on to a prisoner. Can it be set to look for certain things, perhaps to detect only mobile phones?
SG No, there is no difference in the signal from a mobile phone, a knife or a harmless metal object. What we can detect is an increase in signal strength for example, if someone carries a knife and a mobile phone the detected signal will be much stronger than from (say) from a belt buckle.

Broadly what basic scientific principle does the instrument use?
SG It detects the very slight disturbance caused by a metal object to the earth’s magnetic field close to the instrument. Since we are all subjected to the earth’s magnetic field, all the time a protester might find it difficult to make a case.

Is the instrument in operational use anywhere?
SG It is being used in HMPs Belmarsh, Preston, Ashwell, Dover and being considered by a number of others prisons. This is the first custody suite application. It is also being used by a number of police forces; Strathclyde has been using it for over a year and Merseyside police has a prototype for evaluation.

Thank you for explaining it all to me.