  Among various approaches for indirect detection of dark matter, synchrotron
emission due to secondary electrons/positrons produced in galactic WIMPs
annihilation is raising an increasing interest. In this paper we propose a new
method to derive bounds in the mchi - <sigmaA*v> plane by using radio continuum
observations of Messier 33, paying particular attention to a low emitting Radio
Cavity. The comparison of the expected radio emission due to the galactic dark
matter distribution with the observed one provides bounds which are comparable
to those obtained from a similar analysis of the Milky Way. Remarkably, the
present results are simply based on archival data and thus largely improvable
by means of specifically tailored observations. The potentiality of the method
compared with more standard searches is discussed by considering the optimistic
situation of a vanishing flux (within the experimental sensitivity) measured
inside the cavity by a high resolution radio telescope like ALMA. Under the
best conditions our technique is able to produce bounds which are comparable to
the ones expected after five years of Fermi LAT data taking for an hadronic
annihilation channel. Furthermore, it allows to test the hypothesis that space
telescopes like Pamela and Fermi LAT are actually observing electrons and
positrons due to galactic dark matter annihilation into leptons.
