A Security System Using Ultrasound has been proposed in this project. This project was implemented for a low cost security system. In this project the ultrasonic sensors were used to detect the moving object in small place. An ultrasonic transmitter was used which generated and transmitted a 40 KHz signal and an ultrasonic receiver was used which received this transmitted signal which is reflected from any object. A two stage amplifier and a comparator were used to amplify the received weak signal and compare with a reference voltage (5.5V). The comparator’s output (High or Low) was fed to a microcontroller which decided whether to start alarm or not respectively. A buzzer was used to generate an alarm. We tested our project and successfully detected the object within 3 feet. The success rate was above 80%. With proper installation this Security System Using Ultrasound can be used where security break warning is needed.