  Some judiciously chosen local curvature scalars can be used to invariantly
characterize event horizons of black holes in $D > 3$ dimensions, but they fail
for the three dimensional Ba\~nados-Teitelboim-Zanelli (BTZ) black hole since
all curvature invariants are constant. Here we provide an invariant
characterization of the event horizon of the BTZ black hole using the curvature
invariants of codimension one hypersurfaces instead of the full spacetime. Our
method is also applicable to black holes in generic dimensions but is most
efficient in three, four, and five dimensions. We give four dimensional Kerr,
five dimensional Myers-Perry and three dimensional warped-anti-de Sitter, and
the three dimensional asymptotically flat black holes as examples.
