1.       Introduction

Road traffic accidents caused by drunk driving remain a significant global concern, resulting in substantial loss of life, serious injuries, and economic damage every year. Alcohol consumption severely impairs a driver’s cognitive abilities, reaction time, judgment, and motor coordination, thereby increasing the likelihood of accidents [1]. Despite strict traffic regulations, awareness programs, and law enforcement measures, alcohol-impaired driving continues to be a major challenge, especially in developing countries. Conventional preventive approaches, such as roadside breath analyzers and post-incident penalties, are largely reactive in nature and depend heavily on human intervention, which limits their effectiveness in real-time accident prevention [2]. To overcome these limitations, researchers and the automotive industry are increasingly focusing on embedded and intelligent vehicle safety systems that can automatically prevent vehicle operation under unsafe conditions. One such promising approach is the alcohol detection and engine locking system, which ensures that a vehicle cannot be started or operated if the driver is under the influence of alcohol. This proactive safety mechanism directly addresses the root cause of drunk driving by eliminating the possibility of human error at the ignition stage itself.

Recent advancements in microcontroller technology, low-cost gas sensors, and embedded programming have enabled the development of compact, efficient, and affordable alcohol detection systems [3]. The MQ-3 alcohol sensor, known for its high sensitivity to ethanol vapors, has been widely adopted for breath-based alcohol detection applications. When integrated with a microcontroller such as the Arduino Uno, the sensor can continuously monitor alcohol concentration and make real-time decisions based on predefined safety thresholds. The inclusion of a relay-based engine locking mechanism allows safe and reliable control of the vehicle’s ignition system, ensuring electrical isolation between low-voltage control circuits and high-power engine components.

In addition to engine immobilization, audio-visual alert mechanisms such as buzzers and LEDs play a crucial role in enhancing system effectiveness by providing immediate feedback to the driver and nearby individuals [4]. These alerts not only warn the driver about alcohol detection but also support quick diagnosis and system transparency. The use of a DC motor as an engine prototype in experimental setups enables safe demonstration and validation of the system’s operational behavior without involving an actual vehicle. The proposed alcohol detector and engine locking system offers several advantages, including real-time monitoring, low implementation cost, simplicity of design, and ease of integration into existing vehicle architectures. Unlike traditional enforcement-based methods, this system functions independently and continuously, thereby reducing reliance on external monitoring agencies. Furthermore, the modular nature of the system allows future enhancements such as integration with GPS, GSM, biometric authentication, and artificial intelligence-based impairment analysis [5].

This paper presents the design, implementation, and experimental validation of an Arduino-based alcohol detector and engine locking system aimed at preventing drunk driving. The subsequent sections describe the system architecture, hardware components, software implementation, experimental results, and future scope, highlighting the effectiveness of the proposed solution in enhancing road safety and supporting intelligent transportation systems.

2.       Circuit Diagram and Working Principle

The circuit diagram of the alcohol detector and engine locking system using Arduino Uno and an MQ-3 alcohol sensor is shown in Figure 1. The MQ-3 sensor is interfaced with the Arduino through analog pin A0 to continuously monitor alcohol concentration in the driver’s breath, while the Arduino processes this signal and compares it with a predefined threshold value. A relay module connected to a digital output pin of the Arduino controls the engine ignition circuit, represented by a DC motor in the prototype, ensuring electrical isolation and safe switching. When the detected alcohol level exceeds the permissible limit, the Arduino immediately deactivates the relay, cutting off power to the engine, and simultaneously activates a buzzer and LED to provide audio-visual warnings. If no alcohol is detected, the relay remains energized, allowing normal engine operation [6]. The entire system is powered by a regulated supply through a 9V battery and operates in real time, thereby effectively preventing vehicle operation under intoxicated conditions and enhancing overall road safety.

Fig.1. circuit diagram of the alcohol detector and engine locking system [7]

3.       Hardware Components and Description

The hardware components used in the proposed solution for preventing drunk driving are illustrated in Figure 2. The Arduino UNO [Fig. 2(a)] acts as the central control unit that processes sensor data and executes control decisions, while the MQ-3 alcohol sensor [Fig. 2(b)] detects ethanol vapors in the driver’s breath and generates an analog signal proportional to alcohol concentration. A BO DC motor [Fig. 2(c)] is used as an engine prototype to demonstrate vehicle operation, which is controlled through a relay module [Fig. 2(d)] that provides safe electrical isolation between the low-voltage control circuit and the engine system. The BC547 transistor [Fig. 2(e)] functions as a switching and current amplification device, enabling reliable driving of the relay and buzzer from the Arduino output pins [8]. Power to the entire system is supplied by a 9V battery [Fig. 2(f)], while an LED [Fig. 2(g)] and resistor [Fig. 2(h)] together provide a visual indication and current limitation for safe operation. Additionally, a buzzer [Fig. 2(i)] offers audible alerts when alcohol is detected, and the engine is locked. The coordinated operation of these hardware components ensures accurate alcohol detection, immediate engine immobilization, and effective audio-visual warning, thereby forming a reliable embedded system solution for preventing drunk driving [15].

Fig. 2 (a) Arduino UNO             Fig. 2 (b) MQ 3 Sensor

Fig. 2(c) BO Motor                Fig. 2(d) Relay

   Fig. 2(e)BC 547 Transistor       Fig. 2(f) 9V Battery

          Fig. 2 (g) LED                      Fig. 2(h) Resistor

                                     Fig. 2 (i) Buzzer

Fig. 2 Hardware Components [9]

4.       Experimental Results and Observations

The Experimental Setup of Alcohol Detector and Engine Locking System Using Arduino Uno illustrate the practical implementation and testing of the proposed system, as shown in Fig. 3. The experimental setup consists of an Arduino Uno board, MQ-3 alcohol sensor, relay module, buzzer, LED indicators, DC motor (engine prototype), breadboard, and a 9V battery, all interconnected as per the designed circuit [10]. During experimentation, alcohol vapors were introduced near the MQ-3 sensor using a sanitizer bottle to simulate real driving conditions. When alcohol was detected, the sensor output exceeded the predefined threshold value, prompting the Arduino to immediately deactivate the relay, thereby cutting off power to the DC motor and simulating engine locking. Simultaneously, the buzzer sounded, and the LED glowed, providing clear audio-visual alerts. In the absence of alcohol, the relay remained energized, allowing normal motor operation without triggering any alerts. The observed results confirm that the system responds rapidly and accurately to alcohol presence, ensuring reliable engine immobilization and effective warning indication. These experimental observations validate the functionality, responsiveness, and reliability of the proposed drunk-driving prevention system under real-time conditions.

Fig. 3 Experimental Setup of Alcohol Detector and Engine Locking System [14]

5.       Conclusion

The Alcohol Detector and Engine Locking System presented in this paper offers an effective and practical solution to prevent drunk driving. By integrating alcohol sensing with automatic engine control, the system eliminates human error and enforces safety proactively. Experimental validation confirms reliable performance and rapid response. With further enhancements, this system can play a crucial role in intelligent transportation and road safety systems.