In this work, a microcontroller-based voltage monitoring and protection device with user-defined threshold levels is developed. In many developing regions, frequent fluctuations in AC supply and interruptions caused by transient conditions such as lightning strikes, switching surges, and heavy load variations often result in damage to electrical and electronic equipment, and in extreme cases, fire hazards. These irregularities pose a serious reliability challenge in both residential and industrial environments. The proposed design utilizes an Arduino microcontroller to monitor the supply voltage and provide low-cost protection by disconnecting the load whenever voltage levels exceed or fall below user-defined limits. The protection limits can be adjusted by the user according to equipment specifications. The system includes a regulated DC power supply, voltage sensing circuit, control logic, and relay switching stage for isolation of unsafe voltages. Compared with available commercial protective devices that are often expensive and lack user configurability, the developed system offers a more flexible and economical solution. Prototype tests confirm that the system performs effectively, meeting all design objectives for safe operation and equipment protection.