Friday, May 28, 2004

"Lie detectors" and satellite tracking for sex offenders

The BBC reports that Blunkett is considering making sex offenders face compulsory "lie detector" tests and using satellite tracking of offenders.

Now making those convicted of serious offences face some extra hassle on release is not something that bothers me much.

I would hope however that the measures really do make it more difficult/less likely for convicts to reoffend before tax payers money is spent on such things.

But Blunkett's proposals show a touching faith in rather dubious technology. "Lie detectors" are nothing of the sort -- they cannot read minds, they merely measure some proxies for anxiety/stress levels such as pulse rate and sweat.

As for the satellite tracking, shreds this proposal on technical grounds:

This hand waving concept is based on as yet unproven technology, and places an absurd reliance on Global Positioning Satellite and Mobile Phone location technology.

This may eventually work for tracking offenders in the wide open spaces of the USA (but only to the nearest 200 metres or so) where there is a Federally mandated E911 emergency services location infrastructure being built, but this does not exist in the UK.

GPS tracking needs a clear view of at least 4 satellites in the sky i.e. it does not work indoors, and it does not even work in crowded urban areas, where the view is blocked by trees or buildings. Since the GPS satellite signals were never designed to be a security mechanism, they are not two way, so the receivers can be easily spoofed to provide tagged criminals with alibis for their crimes.

Mobile Phone cell location can be several miles out in accuracy, due to the quirks of radio wave propogation and reflection, as demonstrated in the notorious Soham murders case.

Surely this govt wouldn't be stooping to gimmickery, and relying on the public's ignorance of the technical problems behind the proposals, in order to be seen to be "doing something" about crime, would they?

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