As synthetic biology attempts to move into real-world applications, it must confront the additional challenges posed by natural environments such as soil, wastewater, and the gut. Working within the gut microbiome, we sought to increase the range and potential utility of therapeutic probiotics by introducing a simple logic-gate system into the guts of mice and showing that it could work there. We were unsuccessful in this, but along the way explored issues such as what an effective reporter of gene expression that can be detected from within the mammalian gut might look like, and the additional challenges of making genetic circuitry work in stationary-phase. We developed inducible stationary-phase promoters which can be turned on by chemical inducers such as IPTG and aTc, and showed that they express primarily in stationary phase and are more effectively induced when cells are in stationary phase, compared to similar exponential-phase promoters.