In this paper we design and implement an embedded surveillance system by use of multi-frequency ultrasonic sensors with multiple Pyroelectric Infrared sensors (PIR). The ultrasonic sensor module consists of a transmitter and a receiver which are placed in a line; however, ultrasonic sensors with the same frequency are disturbed by crosstalk with each other and have a high miss rate. To overcome these disadvantages of the ultrasonic sensor, we propose the use of improved multi-frequency ultrasonic sensors. In order to reduce the miss rate, both ultrasonic sensors and PIR sensors are managed by the majority voting mechanism (MVM).