Patent ID: 7123145

Claim:
A method for analysing a frequency signal from a movement detector for determining if movement has been detected in an area under surveillance by the movement detector, and for distinguishing a signal resulting from movement from a signal resulting from a spurious source, characterised in that the method comprises the steps of: determining a value of a characteristic of a low frequency component of the frequency signal, comparing the determined value of the characteristic of the low frequency component with a set threshold value of a low frequency alarm threshold for determining if the determined value of the characteristic of the low frequency component is indicative of movement having been detected, determining a value of a characteristic of a high frequency component of the frequency signal to ascertain if the value of the characteristic of the high frequency component is indicative of a signal from a known spurious source having been detected, and setting the low frequency alarm threshold at an intermediate threshold value, if the determined value of the characteristic of the high frequency component is indicative of a signal from a known spurious source, the intermediate threshold value being greater than the value of a corresponding characteristic of a low frequency component of the frequency signal resulting from the signal from the known spurious source for preventing a false alarm.