Background: Security guards play a vital role in ensuring security and order, guarding facilities, and controlling access. Mental workload is a critical variable that influences their performance and well-being, and poor working conditions contribute to mental fatigue and possible errors. Objective: The study aimed to investigate the mental workload of security guards at a university, employing a systemic ergonomics approach and to develop a prototype application that can effectively reduce mental overload, a significant issue in the security guard profession. Materials and methods: The study employed a comprehensive mixed approach. We described the work system using Smith & Carayon’s model, characterized tasks through hierarchical task analysis [HTA], assessed mental workload using the NASA-TLX, and identified errors using the SHERPA method. Results: It was found that the main tasks, such as identity verification, verification of backpack contents, and the decision to enter the campus, present errors that affect performance. The dimensions that generated the greatest mental overload were time demand, mental demand, and frustration. In general, the security guards perceive medium-high levels of mental workload. Conclusions: Identity control tasks for persons entering and leaving the university raise the mental overload being a significant barrier due to constant checks in a short time, which increases mental stress and the possibility of errors. In addition, the absence of advanced technological systems requires verification to be done manually, increasing the workload. We proposed the development of a low-cost application for mobile phones that scans barcodes to enhance efficiency in managing pedestrian flow.