A thermometer capable of automatically switching operational mode, comprising: a control unit configured to determine that the thermometer is to enter or leave from a first mode or a second mode; a power supply unit configured to provide power required by the thermometer ; and a power circuit comprising the power supply unit and electrically connected to the control unit for power supply, and wherein the power circuit comprises a detection unit electrically connected to the power supply unit and the control unit , and the detection unit is configured to detect when the thermometer is shaken from a standing state, and enable the control unit to determine that the thermometer is to leave from the first mode and enter the second mode; wherein a change in voltage level on a pin of the control unit is associated with a shaking state of the thermometer detected by the detection unit ; the thermometer being characterised in that the power circuit comprises a transistor having a collector connected to an operation voltage terminal and the pin, an emitter connected to a ground terminal of the control unit , and a base connected to the operation voltage through a first resistor (R1) and to ground through a second resistor (R2), and a capacitor (C) is connected between the base and the emitter of the transistor, wherein the detection unit and a third resistor (R3) are connected in series between the base and the emitter of the transistor, and the first resistor (R1), the second resistor (R2), the third resistor (R3), and the capacitor (C) are configured to adjust a sensitivity of the detection unit detecting the shaking state. a control unit configured to determine that the thermometer is to enter or leave from a first mode or a second mode; a power supply unit configured to provide power required by the thermometer ; and a power circuit comprising the power supply unit and electrically connected to the control unit for power supply, and wherein the power circuit comprises a detection unit electrically connected to the power supply unit and the control unit , and the detection unit is configured to detect when the thermometer is shaken from a standing state, and enable the control unit to determine that the thermometer is to leave from the first mode and enter the second mode; wherein a change in voltage level on a pin of the control unit is associated with a shaking state of the thermometer detected by the detection unit ; the thermometer being characterised in that the power circuit comprises a transistor having a collector connected to an operation voltage terminal and the pin, an emitter connected to a ground terminal of the control unit , and a base connected to the operation voltage through a first resistor (R1) and to ground through a second resistor (R2), and a capacitor (C) is connected between the base and the emitter of the transistor, wherein the detection unit and a third resistor (R3) are connected in series between the base and the emitter of the transistor, and the first resistor (R1), the second resistor (R2), the third resistor (R3), and the capacitor (C) are configured to adjust a sensitivity of the detection unit detecting the shaking state. <EOS>