  We give a sufficient condition in detecting entanglement resource for perfect
multiqubit teleportation. The criterion involves only local measurements on
some complementary observables and can be experimentally implemented. It is
also a necessary condition for fully separability of multiqubit states.
Moreover, by proving the optimality of teleportation witnesses, we solve the
open problem in [Phys. Rev. A {\bf 86}, 032315 (2012)].
