Southwest B733 at Detroit on Jan 8th 2014, fire indication in cabin

A Southwest Airlines Boeing 737-300, flight WN-685 from Detroit,MI to Baltimore,MD (USA), was climbing out of Detroit's runway 22L when the crew stopped the climb at 6000 feet reporting smoke on board. The aircraft positioned for a return to runway 22L and landed safely about 11 minutes after departure. Emergency services found no trace of fire, heat or smoke, the aircraft taxied to the gate with emergency services following the aircraft.

A passenger reported a strange smell developed on board shortly followed by a fire alarm sounding from the back of the aircraft. The crew subsequently announced there was smoke on the aircraft. Fire fighters entered the aircraft after reaching the gate.