Hot Dot Body Temperature Alert Patch Helps provide an early warning for potentially harmful heat related illness with real-time results Uses thermochromic liquid crystals which are temperature sensitive compounds that temporarily change color with exposure to heat Each quarter-sized, one-time use patch changes color from black to yellow as your body temperature reaches potentially unsafe levels As your body temperature decreases back to a normal range, the patch changes back to black Simply place it on area of skin close to a blood vessel; Features a hypoallergenic adhesive that is water resistant in order to sustain heavy sweat