The Ahwatukee Foothills Family YMCA preschool was evacuated Friday morning when a smoke alarm sounded around 10 a.m. Staff calmly and quickly evacuated the three dozen pre-school students from the facility, located at 1030 E. Liberty Lane, as a precaution. No one was hurt, and students sat patiently in the shade while staff members called parents to pick up their children. "The key is good teachers," said Leean Knox, executive director of the Ahwatukee Foothills YMCA. Firefighters initially thought that a fluorescent light ballast may have overheated and been the cause of the smoke. But according to Capt. Mark Szczepaniec from Engine 46, the culprit turned out to be a burned out motor in a rooftop air-conditioning unit. He said firefighters used a Thermal Imaging Camera to look for hot spots in the lights. When that turned up negative for smoke firefighters went on the roof, checking the air-conditioning units. "There was no real damage other than to the AC unit," Szczepaniec said. Doug Murphy can be reached at (480) 898-7914 or firstname.lastname@example.org.