He has an active interest in short transients in the Universe: sources that appear and disappear within a few days. Triggered by his discovery of optical afterglows to gamma-ray bursts, he is intrigued by the question what else varies in the night at these time scales. To answer this question he was a member of the Palomar Transient Factory collaboration, is part of the Virgo collaboration for gravitational wave detection and he is the PI on both the MeerLICHT telescope as well as the BlackGEM telescope array for the detection of optical counterparts to gravitational wave sources.