What was found
LOSS OF CABIN PRESSURIZATION OCCURRED AFTER TAKEOFF AT 15000 FEET. CABIN ALTITUDE WAS PEGGED OUT AND OXYGEN MASKS WERE DEPLOYED THROUGHOUT CABIN. FLIGHT ATTENDANT ALSO REPORTED SMOKE IN CABIN. CREW DECLARED AN EMERGENCY AND AIRCRAFT WAS RETURNED TO DTW WITHOUT INCIDENT. MAINTENANCE REPLACED LEFT AND RIGHT TURBINE INLET SWITCHES, COMPRESSOR DISCHARGE SWITCHES, PRESSURE CONTROLLER, PRESSURE AMPLIFIER, AND OUTFLOW VALVE ACTUATOR. OPERATIONAL CHECK NORMAL. AIRCRAFT RETURNED TO SERVICE.