We consider a non-conforming stabilized domain
decomposition technique for
the discretization of the three-dimensional Laplace equation.
The aim is to extend the numerical analysis of residual error indicators to
this model problem. Two formulations of the problem are considered
and the error estimators are studied for both. In the
first one, the error estimator provides upper and lower bounds for
the energy norm of the mortar finite element solution whereas in
the second case, it also estimates the error for the Lagrange
multiplier.