An audible alert device determines the effect of environmental factors upon the output sound pressure level of a transducer and establishes drive signal parameters adapted to the current operating environment. A locking tab protrudes upwardly from a motor housing. The loop filter is connected between the output of the phase-locked loop and the input of the variable frequency microwave signal source. A second search process then searches documents at an upper hierarchical level in the same group, thus finding keyword hits in an upper-level document.