This paper introduces a wearable microphone array system designed for health condition monitoring. In particular, the paper presents a novel wheeze signal detection method for wearable systems. The detection method is designed to operate at a sampling rate of 1000 Hz which is way below the typical sampling rate of 44 kHz for audio signals. The detection method is simple and involves only the estimation of the power ratios of selected sub-bands of the signals acquired. The wheeze signal detector has been implemented on a DSP based system. Experimental results show that the proposed detector is able to achieve good accuracy even in the presence of a speech interfering source.