 Abstract engineered bacteria can be used as sensors for detecting chemicals or other stimuli in the environment. These bacteria are equipped with a specialized gene circuit that allows them to distinguish between different types of inputs, such as step inputs, a single event, or pulse inputs, multiple events. This gene circuit is based on unidirectional DNA recombination mediated by phage integrase enzyme, which allows the bacteria to store and read out the sequence of inputs. The resulting data can then be used to infer the order, timing, and duration of the inputs. When combined with single cell analysis, this system can provide valuable insights into how the bacteria respond to various inputs. This article was authored by Victoria Sear, Itaka Hori, Paul W. K. Rothman, and others.