Artificial cells can translate chemical messages to modify the behaviour of bacterial cells and might thus be useful as non-living biological sensors, a new study reports. Lentini et al. generated artificial cells that contained a plasmid construct, the transcription–translation machinery and isopropyl-β-D-1-thiogalactopyranoside (IPTG) encapsulated in a phospholipid vesicle. In co-incubation experiments with Escherichia coli cells, the artificial cells responded to theophylline treatment through their encoded riboswitch to activate expression of a membrane pore protein that resulted in release of IPTG, which diffused into the E. coli cells to modulate transcription.