We humans understand the world through our senses—eyes see light, ears hear sound, skin feels heat or touch.

In the same way, Arduino needs sensors to sense the environment. A sensor is a device that converts real-world signals (like light, distance, or temperature) into numbers that the Arduino can read and process.

For example:

• A Light Sensor (LDR) helps Arduino “see” brightness.

• An Ultrasonic Sensor helps Arduino “measure distance,” just like bats use sound to sense objects.
• A Temperature Sensor helps Arduino “feel” heat or cold.