Synthetically engineered cells are powerful and potentially useful biosensors, but it remains difficult to deploy such systems due to practical difficulties and biosafety concerns. To overcome these hurdles, we developed a microfluidic device that serves as an interface between an engineered cellular system, environment, and user. We created a biodisplay consisting of 768 individually programmable biopixels and demonstrated that it can perform multiplexed, continuous environmental monitoring. The biodisplay detected 10 μg/l sodium-arsenite in tap water using a research grade fluorescent microscope, and reported arsenic contamination down to 20 μg/l with an easy to interpret "skull and crossbones" symbol detectable with a low-cost USB microscope or by eye. No chemical or biological material is released by the biodisplay preventing environmental contamination. The microfluidic biodisplay thus provides a practical solution for the deployment and application of engineered cellular systems.