Abstract: The invention relates to a writing pen with a liquid crystal screen displaying the tested alcohol concentration value, and its architecture includes a lower barrel, an upper barrel, and a sensor device. The sensor device has a circuit board, wherein a sensor, a liquid crystal screen, and a processing unit are installed on and electrically connected to the circuit board. The circuit board receives the alcohol content in the user's exhaled breath and converts it so that a precise value can be displayed on the liquid crystal screen. Hence, a writing pen that can be readily carried and has a liquid crystal screen displaying the tested alcohol concentration value is completed.