What was found
(CAN) FLIGHT CREW RECEIVED A RED SMOKE WARNING MESSAGE IN CLIMB. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED/LANDED WITHOUT FURTHER INCIDENT. INSPECTION OF THE CARGO COMPARTMENT REVEALED NO TRACE OF FIRE OR SMOKE. THE CARGO COMPARTMENT SMOKE DETECTOR SYSTEM WAS DEFERRED IN ACCORDANCE WITH MEL 26-6-4 AND THE AIRCRAFT RELEASED FOR SERVICE. TROUBLESHOOTING REVEALED THAT THE FORWARD SMOKE DETECTOR WAS TESTING SERVICEABLE (SELF-TEST) HOWEVER IT WOULD NOT TRIGGER A SMOKE WARNING WHEN SIMULATING A SMOKE CONDITION. THE DETECTOR WAS REPLACED AND THE SYSTEM TESTED SERVICEABLE. THE MEL WAS CLEARED AND THE AIRCRAFT RELEASED FOR SERVICE. (TC# 20150126004)