To non-contact alarm the sleep apnea under low physical and mental load condition a device was designed including the modules of minimized bio-radar, signal conditioning, control, alarm and power supply, which can realize the function of non-contat detection of the breathing signal, sleep apnea detection and alarm. Experimental results showed that the device can not only non-contact detection the breathing signal without any sensors or electrodes touching the human body, but also has the advantages of smal volume, low power consumption and low price, which may be widely used in monitor the patients with sleep apnea at home or in the hospital.