Devices, methods, and systems for testing a heat detector of a self-testing hazard sensing device are described herein. One device includes a heat detector, and a controller configured to provide energy to the heat detector to heat the heat detector to a threshold temperature, determine an amount of time it takes for the heat detector to heat to the threshold temperature, determine whether the amount of time it takes for the heat detector to heat to the threshold temperature meets or exceeds a threshold amount of time, and determine whether the heat detector is functioning properly based on whether the amount of time it takes for the heat detector to heat to the threshold temperature meets or exceeds the threshold amount of time.