Sensor device having first induction coil set and second induction coil set for determining position change of metal item

A sensor device, which is configured to be disposed on a surface of a side of an object, comprising:

• a casing having a first side that is distant from the object and a second side that is closer than the first side to the object;
• a first induction coil set disposed on the first side;
• a second induction coil set disposed on the second side;
• and
• a control circuit board having a connection line that is electrically connected with the first induction coil set and the second induction coil set, and a microcontroller,
• wherein the microcontroller determines a position change of a metal item disposed on another side of the object according to a physical quantity difference between the first induction coil set and the second induction coil set,
• wherein the second induction coil set is disposed between the object and an exterior wall of the casing facing the object,
• wherein the first induction coil set comprises two coils mounted on two sides of a first substrate, and the second induction coil set comprises another two coils mounted on two sides of a second substrate, and
• wherein a cavity is defined between one of the two coils of the first induction coil set facing the second induction coil set and one of the two coils of the second induction coil set facing the first induction coil set.