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An electronic simulator of physiologic signals used in infant monitoring has been designed, constructed and applied in the Collaborative Home Infant Monitor Evaluation (CHIME). A unique feature of the simulator is that it contains actual physiologic waveforms recorded from infants rather than artificial, idealized signals. The simulator stores breathing waveforms that can be used to test transthoracic-impedance- and inductance-plethysmography-based monitors, and heart rate channels are tested by playing a neonatal QRS complex at preset fixed rates or a variable rate as determined from infant recordings. The transfer characteristics of the simulator are constant over frequencies ranging from 0.5 to 8 Hz for the respiration channels. Data stored in memory are divided into 60 second epochs that can be presented to the monitor being tested in a programmable sequence. A group of 66 CHIME monitors was tested using a simulator programmed with 17 apnoea and bradycardia waveforms. The agreement between monitors as to the duration of detected apnoea decreases as the amount of artefact in the signal increases. Discrepancies between monitors in detecting apnoea duration were found to be similar to inconsistencies between CHIME investigators manually scoring similar waveforms.