The site doesn't really tell how it works. I doubt it is magnetic. It may be capacitative. Search on capaciflector, which has a detection range of about what is claimed. John
Edit: Here are some references from a NASA report. I am reluctant to put the whole report, as it is about 500K.
“Capaciflector Technology Applications,” [Online Document], 2003 Dec 10, [cited 2005 Feb 01], Available HTTP:
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“John Vranish, Electrical Engineer, GODDARD SPACE FLIGHT CENTER,” [Online Document], 1998, [cited 2005 Feb 01], Available HTTP:
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“The "Capaciflector" Proximity Sensor,” [Online Document], Date Unknown, [cited 2005 Feb 01], Available HTTP:
http://www-cdr.stanford.edu/Touch/previous_projects/capaciflector/capaciflector.html
“Capaciflector Technology Description,” [Online Document], 2003 Dec 10, [cited 2005 Feb 01], Available HTTP:
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“Capaciflector Technology Benefits,” [Online Document], 2003 Dec 10, [cited 2005 Feb 01], Available HTTP:
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