Sensor device, holster sensing system, and video-recording system

A video-recording system, comprising:

• a recording device comprising a communication module and a photographing module;
• a holster for accommodating a gun, wherein the gun comprises a sensing metal;
• and
• a sensor device disposed on the holster, wherein the sensor device corresponds in position to the sensing metal when the gun is accommodated into the holster;
• wherein the sensor device comprises:
• a control unit;
• a sensing module electrically connected with the control unit, the sensing module comprising a reference coil set and an induction coil set;
• and
• a power unit electrically connected with the control unit, wherein the power unit is controlled by the control unit to supply current signals to the sensing module, such that the induction coil set and the reference coil set are enabled to induce a magnetic field;
• wherein an inductive area of the reference coil set is smaller than an inductive area of the induction coil set, the induction coil set of the sensing module is adjacent to the holster, and the reference coil set is distant from the holster;
• wherein the control unit determines whether the sensing metal disposed on the gun is present in the holster based on a physical quantity difference between a sensing value generated by the induction coil set and a reference level provided by the reference coil set;
• wherein the sensing metal approaches or moves away from a side of the induction coil set, an inductance generated by the induction coil set is lower or higher than an inductance generated by the reference coil set, and the sensing module receives the physical quantity difference and outputs a sensing result;
• wherein when the sensing result shows that the gun is pulled out of the holster, the control unit transmits a trigger signal to the communication module of the recording device, so as to activate the photographing module to start recording.