To counterbalance human-caused global warming, highly controversial geoengineering techniques, based on stratospheric aerosol injection (SAI), have been proposed as a complement to climate change mitigation. Possible unilateral SAI deployments or tests are a risk. We show that existing satellite instruments do not have the capability to detect unilateral SAI experiments and we propose a future satellite technique, infrared limb emission sounding, that can provide this missing capability.