Dormancy is a sleep-like state of cells that protects them from genetic damage and thus prolongs their survival. This state is reversible and characterized by low metabolic activity and division rate. Researchers from the Leibniz Institute on Aging—Fritz Lipmann Institute (FLI) and the University of Oxford, UK, developed a method to detect dormancy in real time. Using the fluorescence measurement OSCAR (Optical Stem Cell Activity Reporter), cell populations with different dormancy values could be identified and isolated in the small intestine model. OSCAR is thus a suitable tool to better understand the biology of dormant stem cells.