The Extech RH25 pocket-sized heat index psychrometer pen monitors heat index during hot humid days to help prevent heat stroke during outdoor activities, sporting events, or indoor workplaces. Heat Index measures how hot it feels when humidity is combined with temperature, air movement, and radiant heat. Wet Bulb Globe Temperature (WBGT) considers the effects of temperature, humidity, and direct or radiant sunlight.

Built-in multiparameter sensor measures: temperature -4 to 122°F (-20 to 50°C), RH 0 to 99.9%, wet bulb -4 to 122°F, dew point -108.4 to 122°F, heat index -50.8 to 401°F, WBGT -13 to 130°F. Features include user programmable Heat Index/WBGT alarm, min/max/average, data hold, auto power off with disable. Complete with CR2032 battery.