B737 flight crew reported that the cockpit door flew open during takeoff.

Attributes
ACN	1463448
Time
Date	201707
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Takeoff
Flight Plan	IFR
Component
Aircraft Component	Cockpit Door
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 289 Flight Crew Type 10500
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 264 Flight Crew Type 264
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural FAR Deviation - Procedural Published Material / Policy Deviation - Procedural Security Flight Deck / Cabin / Aircraft Event Other / Unknown

Narrative:

We were getting ready to push; running slightly behind schedule. The flight attendant came up with the passenger count napkin and I asked her to flip the cockpit door switch down. She said she would but had a passenger issue she wanted to resolved first. A passenger said that not all of his party was onboard. I had been in the boarding area at about push time to get the weather packet. There were no remaining passengers in the area so I know the agent had not shut the jet way door early. I looked at our time enroute and knew there was no way we could delay any further without being late into ZZZ1. She said she was fine leaving and told the passenger they would have to check with customer service in ZZZ1. We taxied out and departed 4R. On the takeoff roll the cockpit door came open and the flight attendant slammed it back shut immediately. On the climb out we realized the door unlock light was still on thus allowing the door to come open. As soon as it was safe to do so the first officer got up and flipped the switch. He also locked the deadbolt just in case something else might be wrong with it. We inspected the door at ZZZ1 and it worked normally.whenever a checklist is interrupted or not fully completed you must exercise extra vigilance to make sure it gets done. I also am planning on putting the door lights in my scan just before takeoff as an extra safety measure.

Original NASA ASRS Text

Title: B737 flight crew reported that the cockpit door flew open during takeoff.

Narrative: We were getting ready to push; running slightly behind schedule. The Flight Attendant came up with the Passenger count napkin and I asked her to flip the cockpit door switch down. She said she would but had a Passenger issue she wanted to resolved first. A Passenger said that not all of his party was onboard. I had been in the boarding area at about push time to get the weather packet. There were no remaining Passengers in the area so I know the Agent had not shut the jet way door early. I looked at our time enroute and knew there was no way we could delay any further without being late into ZZZ1. She said she was fine leaving and told the Passenger they would have to check with Customer Service in ZZZ1. We taxied out and departed 4R. On the takeoff roll the cockpit door came open and the Flight Attendant slammed it back shut immediately. On the climb out we realized the door unlock light was still on thus allowing the door to come open. As soon as it was safe to do so the FO got up and flipped the switch. He also locked the deadbolt just in case something else might be wrong with it. We inspected the door at ZZZ1 and it worked normally.Whenever a checklist is interrupted or not fully completed you must exercise extra vigilance to make sure it gets done. I also am planning on putting the door lights in my scan just before takeoff as an extra safety measure.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.