Black hole–torus systems may represent astrophysical transient sources powered by the spin energy of a Kerr black hole. Equivalence in poloidal topology to pulsar magnetospheres suggests a long-lived state in suspended accretion when the black hole spins rapidly. The rotational energy is released in several channels: baryon-poor jets along open flux tubes extending from the horizon to infinity, gravitational radiation from the torus, winds and, conceivably, neutrino emissions. Gravitational radiation is expected to be representative of the rotational energy of the black hole, exceeding the output along the open flux tube by some two orders of magnitude. LIGO/VIRGO detections can hereby provide us with a calorimetric test of Kerr black holes.