This study aims to develop a mobile-based electronic repair service application for Prima Service Elektronik to improve the management of customer data, service orders, repair status, service costs, receipts, and transaction reports. The research was motivated by the existing manual process in which customer information and service requests were commonly recorded through telephone and WhatsApp, making data tracking and status monitoring less efficient. The application was developed using the Waterfall model through requirements analysis, system design, implementation, verification, testing, and maintenance stages. Data collection was conducted through observation, interviews, and literature study. The system was designed using Unified Modeling Language (UML) and implemented in Android Studio using Java, with Firebase Authentication and Firebase Realtime Database for authentication and real-time data management. Customer functions include registration, login, service ordering, order history, receipt access, information, and store location. Employee functions include order management, service status updates, service cost and technician notes, receipts, and transaction reports. Black Box Testing showed that the main functions operated according to the defined scenarios, while Compatibility Testing showed good operation on Android 11–14 and limitations on Android 10 and Android 8.1.