An incubator maintains the body temperature of premature newborns through controlled temperature air passed through a chamber housing the baby. The temperature is regulated using a proportional control system that compares the air temperature using a thermistor to a set temperature point. If the air is lower than the set point, a heater is activated in proportion to the difference to precisely control the temperature and minimize overshooting. Some incubators measure skin temperature directly and use radiant warmers with low walls and a heated element above to focus heat on the baby if its surface needs exposure. They also have apnea monitors to sound alarms if respiration ceases for too long.