A hidden sensing device and its urinal are disclosed. The hidden sensing device, which is attached on some sanitary installations, comprises a conductivity sensor for detecting urine and a Micro-programmed Control Unit (MCU) for processing signals, wherein said conductivity sensor has electrodes extending into urine. The device further includes a microwave sensor controlled by the MCU to detect human's movements. When the conductivity sensor has detected urine, the MCU will turn on the microwave sensor to detect the human's presence or departure.