  Observation of lepton number violation would represent a groundbreaking
discovery with profound consequences for fundamental physics and as such, it
has motivated an extensive experimental program searching for neutrinoless
double beta decay. However, the violation of lepton number can be also tested
by a variety of other observables. We focus on the possibilities of probing
this fundamental symmetry within the framework of the Standard Model Effective
Field Theory (SMEFT) beyond the minimal dimension-5. Specifically, we study the
bounds on $\Delta L = 2$ dimension-7 effective operators beyond the electron
flavor imposed by all relevant low-energy observables and confront them with
derived high-energy collider limits. We also discuss how the synergy of the
analyzed multi-frontier observables can play a crucial role in distinguishing
among different dimension-7 SMEFT operators.
