Carbon monoxide detectors in our homes warn of a dangerous buildup of that colorless, odorless gas we normally associate with death. Astronomers, too, have generally assumed that a build-up of carbon monoxide in a planet’s atmosphere would be a sure sign of lifelessness. Now, a UC Riverside-led research team is arguing the opposite: celestial carbon monoxide detectors may actually alert us to a distant world teeming with simple life forms.