Physiological and Cognitive Effects of Alarm Waking and Circadian Disruption: A Case Study on Heart Rate, Core Temperature, and Vigilance

Modern lifestyles often rely on alarm clocks that disrupt the body’s natural sleep-wake cycle, yet their physiological consequences remain underexplored. This case study investigates the effects of alarm-induced waking versus natural waking on key physiological and cognitive parameters: heart rate, core body temperature, and reaction time. Over a two-week observational period, a 21-year-old male participant tracked biometric data during days involving alarm use and days without. Heart rate was measured using a smartwatch, core temperature with an oral thermometer, and cognitive vigilance via reaction-time trials on a mobile app. Results show that alarm-induced waking was associated with higher waking heart rates (mean: 61.5 bpm vs. 58.75 bpm), lower core body temperature (36.4°C vs. 36.55°C), and slower reaction times (mean: 0.372 sec vs. 0.315 sec) compared to free days. Sleep timing analysis revealed approximately 1.5 hours of social jetlag, defined as the discrepancy between mid-sleep time on workdays and free days. These findings suggest that alarm clocks interfere with physiological readiness by interrupting circadian-regulated processes such as thermoregulation, cardiovascular balance, and cognitive arousal. While limited by a single-subject design, this study demonstrates measurable physiological disruption from alarm clock use and reinforces the importance of aligning sleep schedules with biological rhythms.