  Several classes of sources are known to emit different messengers. Among
them, transient sources are a special case, due to their serendipitous
occurrence, time variability and duration on different timescales. They are
associated with explosive and catastrophic events where very compact objects
like neutron stars and black holes are involved. The difficulty of observing
such elusive and possibly short-lasting events requires a fast reaction and a
well-organized alert network between different experiments. In order to
characterize them in the best possible way, instruments with a wide field of
view should serve as external triggers for facilities with small sky coverage.
MAGIC, as a Cherenkov telescope, belongs to the latter category. The search for
transients by MAGIC is possible thanks to an automatic alert system listening
to the alerts sent by the Gamma-ray Coordinate Network (GCN). In this
contribution we describe the MAGIC alert system, which was designed mainly for
the follow-up of Gamma-Ray Bursts in its initial conception. The alert system
was recently updated in a multi-messenger context, receiving alerts also from
neutrino and GW observatories. Finally we will present the MAGIC program for
transient sources and how it was adapted in the current multi-wavelength and
multi-messenger panorama.
