What was found
AT FL 310 CABIN ALTITUDE WARNING LIGHT ILLUMINATED AND HORN SOUNDED, FOLLOWED QUICK ACTIONS ITEMS DECLARED EMERGENCY, IMITATED DESCENT, CABIN PRESSURE WAS CONTROLLABLE IN MANUAL MODE BELOW FL 240. TRANSFERRED TO DMI #73000189 CAT C DUE 4/14/2026 IAW B737 KC2 MEL REF 21-14-1 SPECIAL PROCEDURES 21-14-01, REQUIRED PLACARDS INSTALLED. REF LP 737-004-1462 ITEM #2 R&R CABIN PRESSURE CONTROLLER IAW B737AMM 21-31-21, OPS CHECK GOOD IAW B737 AMM 21-31-00, THIS ACTION CLEARS DMI #73000189, PLACARDS REMOVED.