<p>Fatigue is a critical concern for haul truck operators in the mining industry, and early detection is essential for ensuring safe operations. Advances in wearable technology have made it possible to use smartwatches and applications to monitor an operator’s reaction time continuously during the shift. Smartwatch applications can measure reaction time through simple tests such as a response time test or visual reaction time test. For this study, a custom application was used that displays different colors on the smartwatch’s screen to measure users’ reaction times. The data from these tests were analyzed to determine the operator’s fatigue levels. Results showed that average reaction time slowed by approximately 30 milliseconds during the early morning hours (2–5 AM), corresponding to the circadian trough of alertness. This technology provides a non-intrusive, cost-effective, and continuous measurement of the operator’s reaction time, enabling the detection of early signs of fatigue. This paper explores the feasibility, limitations, and benefits of using smartwatch applications to measure reaction time as a threshold indicator of fatigue in haul truck operators, building on recent advancements in fatigue modeling and monitoring in mining.</p>