B737 CREW GETS CABIN ALT WARNING HORN DURING CLBOUT DUE TO PACK SWITCHES BEING OFF.

Narrative

FO WAS PF. DAY STARTED UNEVENTFUL. ENG START UNEVENTFUL. PASSING 13000 FT THE ALT WARNING HORN ACTIVATED. I LEVELED OFF AS THE CAPT CHKED THE CABIN ALTIMETER. IT READ 10000 FT. CAPT REQUESTED A LEVELOFF AND A DSCNT TO 10000 FT FROM ATC. THE PRESSURIZATION PANEL WAS CHKED AND NOTED THAT THE PACK SWITCHES WERE OFF. I SET THE SWITCHES TO AUTO. THE CABIN ALT STARTED TO COME BACK DOWN. WE RAN THE QRH BEFORE CONTINUING OUR CLB. AFTER BEATING OURSELVES OVER THE HEAD ABOUT CHKLIST DISCIPLINE AND HOW MANY TIMES WE LOOKED BUT DID NOT SEE; IT CAME DOWN TO 'I' MISSED THE PACK SWITCHES 3 TIMES. ONCE AFTER START; ONCE BEFORE TKOF; AND ONCE DURING THE 10000 FT CHK. AFTER THE ENG START CHKLIST WHILE I WAS ACCOMPLISHING MY AFTER START FLOW; THE CAPT TURNED OFF THE COCKPIT LIGHT. THE COCKPIT WAS TOTALLY DARK AND I ASKED IF I COULD TURN ON THE LIGHT AGAIN. I THEN FAILED TO SET THE PACKS TO AUTO. THE NEXT OPPORTUNITY TO CATCH THE SWITCHES WAS THE BEFORE TKOF CHK. WE HAD JUST STARTED RUNNING THE CHKLIST WHEN TWR ASKED US TO PULL UP TO #1. THE ITEM WAS CALLED FROM THE CHKLIST AND AGAIN WITH A DARK COCKPIT; I LOOKED AT THE PANEL BUT DID NOT SEE; AND ACCEPTED THE APPROPRIATE RESPONSE. WITH THE CLB CHK STILL TO COME; IT IS HARD TO BELIEVE THAT THIS ITEM WAS MISSED A THIRD TIME. THIS SHOULD HAVE BEEN THE PLACE TO FIND THE ERROR; ACFT PRESSURIZATION AND THE PACK SWITCHES; ALONG WITH CONFIRMING THE CABIN TEMP; WHICH; IRONICALLY; WAS ACCOMPLISHED. THERE IS NO EXCUSE THAT CAN JUSTIFY MY ACTIONS EXCEPT FOR THE INITIAL INTERRUPTION AND COMPLACENCY. I'VE READ SAFETY RPTS; AND THEY HAVE BEEN VERY HELPFUL. I AM JUST ASHAMED THAT I DIDN'T DO WHAT I WAS SUPPOSED TO DO. AND YES; THE CABIN ALT WARNING HORN DOES SOUND LIKE THE GEAR WARNING HORN. FOLLOWING COMPANY POLICY ON CHKLIST DISCIPLINE WILL ELIMINATE THIS EVENT IN THE FUTURE. PAYING LIP SVC GETS YOU NOWHERE. CALL FOR AN ITEM ON THE CHKLIST; LISTEN TO THE RESPONSE; AND VERIFY THE POS OF THE SWITCH.