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In this paper we design and implement a surveillance system based on an embedded system with multiple Pyroelectric Infrared sensors (PIR) to enhance the reliability. The sensing reliability of a PIR sensor decreases when the distance from the object has increased or the ambient temperature has risen. Our design integrates multiple sensors to construct a sensor group and count their states by using a majority voting mechanism (MVM). If over half the sensors in a sensor group sense a temperature change, the majority voting circuit sends a trigger signal to the surveillance system. On the other hand, the majority voting circuit does not send the trigger signal if fewer than half the sensors sense any temperature change. This method is helpful in decreasing the miss rate of a surveillance system because the majority compensates for sensing errors and thus enhances the reliability of a surveillance system in the monitoring area. Both the mathematical equation and the sensing experiment show that we improve the reliability.