What was found
FLIGHT 200, REPOSITION FLIGHT GEG - AFW/AIR TURNBACK DISCREPANCY: IN CRUISE, A REAR CABIN DOOR UNLOCK LIGHT ILLUMINATED. DECLARED AN EMERGENCY AND ON DESCENT, PULLED O2 MASKS. INTERCOM ON MASKS INOP. ESTABLISHED COMMUNICATION WITH ATC WITH HANDHELD RADIO. RETURNED TO GEG AND LANDED SAFELY. CORRECTIVE ACTION: ADJUSTED DOOR MICROSWITCHES, REPLACED THE CABIN DOOR CAUTION RELAY AND BOTH O2 MASKS. OPS CHECKS GOOD.