Low frequency alarm tones emitted by life safety devices are more likely to notify sleeping children and the elderly. Disclosed herein is a life safety device equipped with a novel, compact, circumferential resonant cavity which increases the low frequency (400-600 Hz square wave) acoustic efficiency of an audio output apparatus formed by acoustically coupling an audio output transducer to the resonant cavity. The resonant cavity is a compact circumferential acoustic resonator with a captured mass of air within a ring shaped cavity significantly reducing the overall size of the resonator, thereby permitting the audio output apparatus to fit within the housing of conventional size life safety devices such as, but not limited to, residential and commercial smoke alarms and carbon monoxide alarms. The compact resonator is an acoustic compliant cavity with internal passages transforming axial traveling sound waves to circumferentially traveling sound waves thereby yielding a very compact geometry.