The Kestrel 5400 is revolutionary in size, cost and capability for those in need of measuring Heat Stress. Along with having a Wet Bulb Global Temperature reading, the Kestrel 5400 displays thermal work limit (“TWL”), another recognized composite heat stress prediction tool. For both WBGT and TWL, the Kestrel 5400 provides on-screen alarms when conditions enter the caution and danger zones, providing clear and immediate guidance that heat illness prevention steps must be taken. The Kestrel 5400 also displays natural wet bulb temperature, and black globe temperature.