The Double Sensor examined in this trial was developed by Dräger Company and is a novel non- invasive device for assessing core body temperature. In a preliminary research investigators have conducted the Double Sensor was found promising for potential use of physiological heat stress early detection. This follow-up experiment was designed to validate the data during high and changing body core temperatures and to examine the Double Sensor performance while integrated into a helmet as in intended application.

12 healthy civilian volunteers will arrive to our lab and will undergo 4 experiment days: Recruitment day + VO2max test, 3 random days performing experiment protocol, dressed in uniforms: sitting in thermoneutral condition for one hour, afterwards they will walk on a treadmill in 5.5 km/h and 4% incline in hot chamber (40% celsius and 40% relative humidity) for 1.5 hours. Once connected to rectal thermistor and to the Double Sensor attached to the skin surface by sticker, once same as the day before with addition of cooling system of Icetron Technologies Ltd. worn on the wrist, and once connected to rectal thermistor and to the Double Sensor integrated into a helmet.

Inclusion Criteria:

• Aged 18-40 years.
• Healthy civilian volunteers.
• Without known medical illness or medication use.

Exclusion Criteria:

• History of heat injury.
• The existence or suspicion of existing cardiac or respiratory disease.
• Diabetes.
• Obesity.
• Infectious disease 3 days prior to the experiment.