Abstract In this work, we present the design of an ultra-fast IR (InfraRed) detector for the search of astronomical transients. Time-domain astronomy is a field in continuous growth in the last years, with interest in detectors with nanosecond performance, in order to observe potential fast transients with the time scale of GRBs (Gamma Ray Bursts) and FRBs (Fast Radio Bursts). An ultra-fast temporal detector based on HgCdTe photoconductors is under development in Italy, at the Frascati National Laboratory of the National Institute of Nuclear Physics, by tests at SINBAD, the DAFNE infrared beamline. The detector will be used for mid-IR observations together with a ground-based reflecting telescope or launched on a scientific balloon.