It seems you're referring to a computer mouse that doesn't have a red light or an optical sensor at the bottom. In such cases, the mouse is likely using a different technology called a trackball.
A trackball mouse operates differently from a traditional optical mouse. Instead of moving the mouse across a surface, you use your fingers to roll a ball located on the top of the mouse. The trackball detects the movement of the ball and translates it into cursor movement on the computer screen.
Inside the trackball mouse, there are sensors that detect the rotation of the ball. These sensors track the movement and direction in which the ball is rolled. As you move the ball with your fingers, the sensors measure the rotational changes and send the corresponding signals to the computer.
The advantage of a trackball mouse is that it allows for precise cursor control without the need for physical movement of the entire mouse across a surface. It can be particularly useful in situations where you have limited desk space or when fine control is required, such as in graphic design or gaming.
While trackball mice may be less common than traditional optical mice, they offer an alternative input method for navigating a computer screen. They eliminate the need for a red light or optical sensor on the bottom of the mouse because the movement is detected directly through the rotation of the trackball itself.