EMB ERJ 170/175 ER/LR
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Deck / Cabin / Aircraft Event Passenger Misconduct; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
General None Reported / Taken
Human Factors; Procedure
In cruise flight; crew heard lavatory smoke detector go off and shortly after we received a Master Warning 'LAV SMOKE' indication. This lasted for 5-10 seconds. Crew donned O2 masks and by the time we had them on the indication disappeared. I called the flight attendant who said a passenger had been in the lav. When she opened the door; the passenger appeared startled and asked what the noise was. She replied it was the smoke detector and asked him if he was smoking or vaping. The passenger was seated in first class; seat XY; and was quoted saying 'I fly you guys all the time; I would never smoke in the lav.'The flight attendant checked the lavatory and could not find the source of the smoke; she also checked the trash bin. The flight attendant asked this passenger a few more times later if he set the alarm off and he continued to deny. The flight attendant did not catch him in the act nor saw any smoke/vape product on the individual.Flight continued safely to destination at my discretion. I had previously observed a passenger blow a cloud of vape while in the jetbridge in ZZZ prior to boarding our flight. We determined this was the same person. I did not get a chance to question the individual as he took off as soon as the door opened. While on the crew van; the same person in question was seen; in a waiting area; vaping.I should've asked Dispatch for their opinion and possibly had law enforcement meet us on the ground; conduct a search of the passenger; and determine if he broke policy. I also should've called the duty officer to ask their opinion. I was searching for guidance on passenger enforcement; but could not find any.
EMB-175 Captain reported a passenger activated the lavatory smoke detector while vaping in flight.