A new device from Lincoln Laboratory can now alert trainees when they are heading toward injury. The device continuously estimates a person’s core body temperature to determine their risk level for heat strain as they train. This risk is communicated on a smartwatch display, providing early warning to its wearer.

James Balcius tests the heat strain detection device. The smartwatch displays a thumbs up and green background, indicating that he is not at risk of heat injury at this time. (Image: MIT)

The system is made up of a few components. First, an armband sensor measures the trainee’s heart rate. Those heart rate data are sent via Bluetooth to a smart-watch. Installed on the watch, a Laboratory-developed app runs an algorithm that uses the data to estimate core body temperature. Depending on those results, the smartwatch will display a visual icon (a stop sign, danger sign, or thumbs up) with a colored background (red, yellow, or green) and emit an audible tone to alert users if they are overheating.

“The core body temperatures that the device monitors to determine a red, yellow, or green alert are set at generally lower temperatures, appropriate for recruits who may not yet be acclimated to the demands of military training. In the future, this setting could be modified at the individual level,” said James Balcius, a biomedical researcher in the Human Health and Performance Systems Group, who leads the research.

The algorithm this device uses to estimate core body temperature was developed by the U.S. government in 2013. It has since been used in many commercial products. This device, however, is the first use of the algorithm in a form factor as small as a smartwatch.

This technology was developed under the sponsorship of the U.S. Army Medical Materiel Development Activity and in partnership with the U.S. Army Research Institute of Environmental Medicine. In October 2021, the technology was transitioned to the U.S. Marine Corps Training and Education Command, who have so far fielded 170 prototypes at basic training sites. Feedback has been positive, with recommendations to enhance the capability.

Balcius is now pursuing ways to transition this capability beyond the military. Heat stress injuries are reported significantly in humanitarian aid and disaster relief organizations as well.

For more information, contact David R. Granchelli at This email address is being protected from spambots. You need JavaScript enabled to view it.; 781- 981- 4204.