  Black hole bombs are usually constructed by surrounding an ergoregion by a
mirror. The fields propagating between the event horizon and the mirror are
prevented from escaping to infinity and reflected back to the ergoregion, thus
undergoing repeated superradiant scattering which leads to a linear
instability. We introduce a new construction in which the field is outside the
mirror and is therefore prevented from falling into the black hole but is free
to escape to infinity. Provided the mirror is inside the ergoregion, it turns
out that this still causes linear instabilities. This behaviour is observed on
Reissner-Nordstrom and de Sitter-Reissner-Nordstrom backgrounds using numerical
simulations, based on a semi-implicit discretisation on a first-order system
formulation of the partial differential equations governing the evolution of
the scalar field. We also perform simulations for a standard black hole bomb
and for another type of contraption: a sandwich black hole bomb.
