  Majorons are (pseudo-)Nambu-Goldstone bosons associated with lepton number
symmetry breaking due to the Majorana mass term of neutrinos introduced in the
seesaw mechanism. They are good dark matter candidates since their lifetime is
suppressed by the lepton number breaking scale. We update constraints and
discuss future prospects on majoron dark matter in the singlet majoron models
based on neutrino, gamma-ray, and cosmic-ray telescopes in the mass region of
MeV--10 TeV.
