There are gravitational wave observatories all over the world that astronomers use in order to aide them in detecting gravitational waves. There are different machines that act as detectors. These machines advance and get better at doing this job almost daily. There is always a new machine arriving that can do this better.
Currently the most sensitive detector is LIGO the laser Interferometer gravitational wave observatory. Ligo can detect pretty small gravitational waves. Even with how sensitive LIGO is it is only a matter of time before there is an even more powerful and more precise detector.