This is an Arduino-based Proximity Sensor circuit wired ... see the burning eye of the red LED when there is no object in the safe-zone (within 5 cm from the HC-SR04 module), and an ear-splitting beep ...

To supply targeting data for the launcher, an Arduino Uno uses an ultrasonic sensor pair mounted atop a servo. As the servo rotates, the returns from the ultrasonic sensor are plotted on a screen ...