Majorons are the Goldstone bosons associated to lepton number and thus closely connected to Majorana neutrino masses. At tree level, its only fermion couplings are to neutrinos. Couplings to charged fermions arise at one-loop level, including lepton-flavor-violating ones that lead to decays \(\ell\to \ell' J\), whereas a coupling to photons is generated at two loops. The typically small couplings make massive majorons a prime candidate for long-lived dark matter. Its signature decay into two mono-energetic neutrinos is potentially detectable for majoron masses above MeV and most importantly depends on different parameters than the visible decay channels.