NIOSH and OSHA recently released the redesigned, co-branded OSHA-NIOSH Heat Safety Tool App. This version replaces the app previously created by OSHA in 2011. The app calculates the heat index at outdoor worksites using the smartphone’s geolocation capabilities to pull current weather conditions from the National Oceanic and Atmospheric Administration (NOAA) satellites. Based on the calculated heat index, users are provided specific sets of recommendations for protections against the heat. Workers and managers can use these recommendations to adjust their work environment. The app recommendations were updated to reflect information found in the NIOSH Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (published in 2016). Along with updated recommendations, the co-branded app has new features and improved usability. With a basic understanding of the heat index, the app is a useful tool for working safely outdoors.