Abstract: A mechanism mounted adjacent one end of a roller bearing carries a probe biased against ends of the rollers, the probe having a shoe wide enough to span at least two rollers. A spring biased hammer is latched in a cocked condition by a latch device which is controlled by the probe. A bell or sounder rotates in a path near the hammer. When the cage of the bearing fails prior to bearing failure, the rollers bunch up forming a gap which allows the probe to drop into the gap to unlatch the hammer which swings against the bell to cause an audible indication of imminent bearing failure.