Patent ID: 7038449

Claim:
A detection device for detecting a strength of a magnetic field of an object, comprising: a housing having a center, a first end and a detection end; a permanent magnetic element suspended above the center of the housing so as to rotate freely about the center, said permanent magnetic element having: a first magnetic field strength; and an indicator; a biasing permanent magnetic element disposed at the first end of the housing and having a second magnetic field strength for biasing the indicator toward the first end; a first distance between the permanent magnetic element and the biasing permanent magnetic element; and a threshold magnetic field strength being determined from the first magnetic field strength, the second magnetic field strength and the first distance, said threshold magnetic field strength is greater than or equal to 10 gauss; wherein when the object is placed approximate to the detection end and the object magnetic field strength is greater than the threshold magnetic field strength, the indicator rotates toward the detection end.