B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 216
Confusion
Aircraft Equipment Problem Less Severe
Flight Crew Rejected Takeoff
Human Factors
Pushback was normal except ATC advised that 19R was the new departure runway. I went ahead with the engine start while Captain worked on runway change with performance computer.  All checklists were completed and complied with as normal. Taxi out was uneventful with Before Takeoff Checklist completed in timely manner. Cleared for takeoff on 19R; Captain advanced thrust levers to takeoff N1s and Configuration horns sounds. We both check all settings and do not notice any abnormalities.  Captain aborts takeoff; speed was less than 60 knots. We tell ATC of abort; clear runway; and check all settings. Captain believed speedbrake not in down detent on taxi rollout on runway.   Not sure; but throttle burst check may not been advanced far enough?
B-737 crew aborted the takeoff due to configuration horn activation at thrust lever advancement. No abnormalities found. Crew suspects that the speedbrake lever was not completely stowed.