How to detect a key pressed in a keypad?

To detect a key pressed on a keypad, you can use a microcontroller with input pins connected to the rows and columns of the keypad matrix. When a key is pressed, it completes a circuit between a specific row and column, allowing you to identify the key. You can implement a scanning method where you set one row low at a time and read the columns to see which key is pressed. Libraries or code for specific microcontrollers can simplify this process, making it easier to implement key detection.