The HC-SR04 ultrasonic distance sensor offers non-contact range measurement from 2 cm up to 400 cm with high accuracy and stable readings. Operating at 40 kHz, it emits sonic pulses and measures the round-trip time required for the echo signal to return. It connects via standard 4-pin headers (VCC, Trig, Echo, GND) and provides a straight-forward interface for microcontrollers. Widely used in distance-measuring tools, smart parking assistants, automated liquid level indicators, and mobile robot navigation systems.