BACKGROUND: Core temperature information is important for guiding prevention and treatment measures. It is critical for those working in severe environments, such as firefighters, military, law enforcement, and construction and farm workers. Development of new physiological monitoring tools that are easy to use and provide reliable core temperature information is critical for heat injury prevention. Currently, less invasive core temperature monitoring tools come with significant accuracy limitations, whereas more accurate devices are difficult to use in the field. An easily wearable sensor that correctly estimates core temperature could prevent heat injuries and deaths. The ThriveHRI sensor system is being developed for use in a smartwatch platform. The current study compared the ThriveHRI sensor/smartwatch to an Equivial LifeMonitor and a rectal thermistor. The purpose of this study was to determine if the ThriveHRI sensor system provides an accurate and precise estimate of core temperature at rest and during physical activity representing firefighter occupational tasks at elevated temperatures in healthy adults. METHODS: Twenty-five healthy, physically active adults between the ages of 19-45 years volunteered. Participants completed multiple rounds of deadlifting and treadmill walking in an environmental chamber set to 43.3°C (115°F) and 50% relative humidity. Core temperature was monitored continuously via a Datatherm rectal thermometer, Equivital Eq02+LifeMonitor, and a ThriveHRI heat watch. RESULTS: No significant difference in accuracy between devices was found for any condition (ps ≥ 0.532). A significant difference in bias between devices was found for easy walking (t(21) = 5.55, p < 0.001, g = 1.01), deadlift (t(19) = 3.60, p = 0.002, g = 0.73), and treadmill (t(16) = 2.42, p = 0.028, g = 0.60). A significant difference in precision between devices was found for easy walking (t(21) = 4.23, p < 0.001, g = 1.21), but no significant difference in precision between devices was found for deadlift, or treadmill (ps ≥ 0.067). CONCLUSIONS: This study demonstrates that the agreeability between the Equivital EQ02+ LifeMonitor, ThriveHRI sensor, and the rectal thermometer remains consistent as core temperature increases and exposure to a heated environment is sustained. The ThriveHRI heat watch system may be an accurate and precise core temperature sensor system for use in the field.

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