A detection device and method commonly used for a video interface outlet and earphone line outlet is used to allow the detection device to detect whether a three- or four-terminals plug is inserted in the outlet. The detection device detects whether the impedance value of the video output terminal of the plug is larger than the preset value. If yes, the detection device control a video signal output terminal to output a video signal. If the impedance is not larger than the preset value, the detection device then controls the video signal output not to output a video signal and only to output an audio signal.