ABSTRACT Batac, Justin Dale C., Matias, Christian L., Torres Arjay Ryan S. Department Computer Studies and Automation, College of Engineering and Computer Studies, Pampanga State Agricultural University, June 2023"ARDUINO-BASED ALCOHOL BREATHALYZER DETECTOR WITH MOBILE APPLICATION" Adviser: Prof. Aloysius S. Valerio A breathalyzer is a diagnostic device that measures how much alcohol is in the air a person breathes out. It can be used to estimate blood alcohol content (BAC), Or how much alcohol is in the blood. Despite all the warnings regarding drunk driving accidents. People still tend to drive while intoxicated even though they know it can lead to accidents. The Sacop Homes in Magalang, Pampanga is dealing with an issue involving drunk drivers entering the subdivision. The study titled "Arduino- Based Alcohol Breathalyzer Detector with Mobile Application" seeks to offer a solution to this problem. The objective is to develop a system that utilizes an Arduino microcontroller, an alcohol sensor module, and a mobile application to address the detection of alcohol levels in individuals attempting to enter the subdivision. By implementing this system, the study aims to effectively identify and prevent drunk drivers from gaining access to the subdivision, thereby promoting safety within the community and acting as a deterrent against driving under the influence of alcohol. Through the development of the study, researchers used the SDLC's agile model, is a methodology that provides a method for developing the system that is well-structured and defined. Use Case Diagram, System Flowchart, Context Diagram to examine anddetermine the flow and output of the program. MIT APP Inventor and Arduino IDE is also use to develop an application for the project. The data gathering process questionnaires, and conducting internet research. The questionnaires were analyzed using statistical procedures to interpret the primary data collected. To determine the required number of respondents, Slovin's formula was employed as the method. involved conducting interviews, administering A questionnaire has been distributed in the subdivision to 172 user, and (3) IT experts to evaluate system's performance. A cumulative score and descriptive writing was used to interpret the data. Base on evaluation most of the respondents evaluated the systems performance is "Strongly Agree", receiveda score of 3.76 and 3.69 for IT experts, indicating that system meets the required functions and support the users' needs.