Prediction of the detectability of well‐defined signals in steady‐state background noises are based on considerable theory and much practical experience. Little information is presently available to support predictions of detectability of complex signals in time‐varying noise environments. The current study has temporal variability of background noise is long with respect to signal duration, observers' detection performance improves in more highly variable noise environments of constant average energy. Observers detecting a sinusoid embedded in one‐third‐octave band of Gaussian noise in a two alternative forced‐choice task produced psychometric functions characterized by higherd′ values for increasingly variable background noises, relative to performance in steady‐state noise.