When a red giant star collaps on itself a burst of neutrinos is produced. This occurs before that light is emitted in the explosion, The SuperNova Early Warning System (SNEWS) is a network of neutrino detectors designed to give an early warning to astronomers of a supernova event in the Milky Way. The neutrino pulse from supernova 1987A was detected 3 hours before the photons.
The current members of SNEWS are Borexino, Super-Kamiokande, LVD, SNO and IceCube.
http://en.wikipedia.org/wiki/Supernova_Early_Warning_System
