Abstract: A magnetic hole finder arrangement having a test field detector including a GMR sensor and may having a test field detector including a first and second magnetic field detectors (which may be GMRs) arranged with respect to a hole location position, the detectors having magnetic axes each arranged transversely to a radius from the hole location position to the detector. The arrangement may include geomagnetic or ambient magnetic field compensation.

Abstract: A method for product authentication, comprising applying to the genuine products code on a label, the code being generated by an algorithm, which code is unique to a small sub-set of articles, preferably for a single such article, so that it can be assumed that any product on the market which either does not have a label or has a wrong label, or for which the label is otherwise accounted for, is counterfeit, the label being machine readable, such as a writeable RFID tag characterised in that the label comprises a machine-readable microcircuit to which a code can be written, and from which the written code can be read remotely.

Abstract: A system for authenticating re-presentable items, such as currency notes and passports, comprises applying to each item a unique code, reading the code on presentation, and checking the code against a database, characterised in that at each check, the code is altered.