Narrative:

1.5 hours into flight I was informed that a passenger reported smoke rising from below [the] seat. The inflight entertainment (ife) box below the seat appeared to be the source of the smoke. The flight attendants moved the passenger and used a halon extinguisher on the ife box below the seat. I decided to run the QRH smoke; fire or fumes checklist. I instructed the flight attendants to turn off the ife; power port; and internet switches.the smoke appeared to decrease; however I was uncomfortable continuing the flight with a possible ife related electrical/smoke problem. I decided a diversion was in order. I decided on a diversion to [a suitable alternate]. I [advised] ATC and requested direct routing. I sent emergency and diversion ACARS messages to dispatch. I briefed the flight attendants; made a PA to the passengers; and made contact with operations. I elected to fly the overweight landing. We landed without incident.aircraft rescue and fire fighting (arff) followed us to the gate. Once the jet bridge was brought to the aircraft; arff boarded and inspected the area around seat 20 B. Their thermal sensors showed no hotspots. I decided to have the passengers exit into the terminal and await further instructions. I coordinated with maintenance and dispatch. Contract maintenance arrived within 30 minutes. My crew and I were comfortable continuing if the entire ife system was disabled and placarded inoperative. We also needed an overweight landing inspection and a replacement halon extinguisher. In the end; the aircraft was taken out of service due to the lack of a replacement halon extinguisher. We were rescheduled to depart later in the day and sent to the airport hotel for crew rest.I would like to commend [the] first officer for outstanding airmanship and professionalism in assisting me during this time-compressed emergency.additionally I want to commend [the] flight attendants for their professionalism and skill in handling a difficult situation. Their actions addressing the smoking ife equipment quickly defused what could have become a dangerous situation.

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Original NASA ASRS Text

Title: B737-800 flight crew reported diverting to an alternate airport after smoke in the cabin was traced to the inflight entertainment box below a passenger seat.

Narrative: 1.5 hours into flight I was informed that a passenger reported smoke rising from below [the] seat. The Inflight Entertainment (IFE) box below the seat appeared to be the source of the smoke. The flight attendants moved the passenger and used a Halon extinguisher on the IFE box below the seat. I decided to run the QRH smoke; fire or fumes checklist. I instructed the flight attendants to turn off the IFE; power port; and internet switches.The smoke appeared to decrease; however I was uncomfortable continuing the flight with a possible IFE related electrical/smoke problem. I decided a diversion was in order. I decided on a diversion to [a suitable alternate]. I [advised] ATC and requested direct routing. I sent emergency and diversion ACARS messages to Dispatch. I briefed the flight attendants; made a PA to the passengers; and made contact with operations. I elected to fly the overweight landing. We landed without incident.Aircraft Rescue and Fire Fighting (ARFF) followed us to the gate. Once the jet bridge was brought to the aircraft; ARFF boarded and inspected the area around seat 20 B. Their thermal sensors showed no hotspots. I decided to have the passengers exit into the terminal and await further instructions. I coordinated with Maintenance and Dispatch. Contract maintenance arrived within 30 minutes. My crew and I were comfortable continuing if the entire IFE system was disabled and placarded inoperative. We also needed an overweight landing inspection and a replacement Halon extinguisher. In the end; the aircraft was taken out of service due to the lack of a replacement Halon extinguisher. We were rescheduled to depart later in the day and sent to the airport hotel for crew rest.I would like to commend [the] First Officer for outstanding airmanship and professionalism in assisting me during this time-compressed emergency.Additionally I want to commend [the] flight attendants for their professionalism and skill in handling a difficult situation. Their actions addressing the smoking IFE equipment quickly defused what could have become a dangerous situation.

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.