The increase in criminal activities has led to a growing demand for advanced smart home security solutions. Ensuring safety, especially when away from home, necessitates the integration of reliable, cost-effective security systems. This paper presents the design and implementation of a smart home security system that leverages an Arduino microcontroller and a GSM (Global System for Mobile Communications) module. The primary objective of the system is to enhance home security by promptly notifying homeowners of unauthorized entry or motion. The system integrates an Arduino UNO microcontroller with a PIR (Passive Infra-Red) motion sensor and a GSM module. Upon detecting motion or unauthorized access, the system uses the GSM module to send alerts to the homeowner's mobile phone, while simultaneously activating a buzzer and LED indicators. The solution is designed to be both affordable and accessible, utilizing basic, readily available components. This paper includes a detailed software implementation through Arduino programming and outlines the hardware configuration, including circuit diagrams and component specifications. The system’s reliability and performance in detecting intrusions are validated through various testing scenarios.