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In this paper we design and implement a surveillance system based on an embedded system with multiple ultrasonic sensor modules to enhance the system's reliability. The ultrasonic sensor module includes a transmitter and a receiver, and they are placed in a line direction. Because the ultrasonic air transmission will spread a beam angle, we use multiple ultrasonic receivers to receive the ultrasonic transmission. If any intruder passes through the ultrasonic sensing area, the ultrasonic transmission will be blocked by a human body. As the receivers will not receive any ultrasonic transmission produced by the ultrasonic transmitter, the system will sense when someone has passed through the surveillance area. We use a Majority Voting Mechanism (MVM) for a group of sensors. If over half the sensors in a sensor group sense a signal blocking, then the majority voting circuit will send a trigger signal to the surveillance system.