Temperature is a key parameter to regulate cell function, and biochemical reactions inside a cell in turn affect the intracellular temperature. It's vitally necessary to measure cellular temperature to provide sufficient information to fully understand life science, while the conventional methods are incompetent. Over the last decade, many ingenious thermometers have been developed with the help of nanotechnology, and real‐time intracellular temperature measurement at the micro/nanoscale has been realized with high temporal‐spatial resolution. With the help of these techniques, several mechanisms of thermogenesis inside cells have been investigated, even in subcellular organelles. Here, current developments in cellular thermometers are highlighted, and a picture of their applications in cell biology is presented. In particular, temperature measurement principle, thermometer design and latest achievements are also introduced. Finally, the existing opportunities and challenges in this ongoing field are discussed. Cellular thermometers flourished in the last decade under the inspiration of exploring the mechanisms of cell activities through intracellular temperature. Various strategies based on nanotechnology have been proposed to realize real‐time intracellular temperature measurements with high temporal‐spatial resolution. A comprehensive review of the recent achievements, existing challenges, and future prospects of cellular thermometers is provided.