Human body detecting device

A human body detecting device, comprising:

• a pyroelectric infrared radial (PIR) sensor configured to sense infrared radiation and then generate an electronic signal based on the sensed infrared radiation;
• a thermometer configured to sense an ambient temperature and then generate a temperature value;
• a microprocessor electrically connected to the thermometer;
• an amplifying unit electrically connected to the PIR sensor and the microprocessor;
• and
• a plurality of amplification adjusting units electrically connected to the microprocessor and the amplifying unit and corresponding to a plurality of temperature intervals, each amplification adjusting unit comprising:
• a switch, an enable end of the switch electrically connected to the microprocessor;
• and
• a resistor electrically connected to the signal amplifier, the switch, and the voltage-dividing resistor, wherein when a resistance of the resistor in the enabled amplification adjusting unit is decreased, an amplifier gain of the electronic signal increases,
• wherein the microprocessor selects to enable one of the amplification adjusting units based on a comparison between the temperature value and the temperature intervals, whereby the electrical signal is modulated by the amplifying unit according to the enabled amplification adjusting unit.