Q400
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Workload; Time Pressure
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Inflight Event / Encounter Other / Unknown
Air Traffic Control Provided Assistance; Aircraft Equipment Problem Dissipated; Flight Crew Landed As Precaution; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed
Aircraft
My Captain and I were ferrying an aircraft from ZZZ-ZZZ1. We were taking off Runway XX and after takeoff our lavatory smoke detector alarm started beeping. After direction from the Captain we [advised ATC] and made the decision to return to ZZZ. We requested direct ZZZ to hold and set up for our return. As we were entering the hold the alarm had stopped; we decided to still return to ZZZ as it was the safest decision and we could not verify that there was no fire. As we were holding we set the aircraft up to return; calling Company and following procedures for our return. After we finished setting ourselves up and getting ready we ran the checklists that we needed to; we requested vectors for to return to ZZZ and requested an ILS. We returned to ZZZ without any further issue and had fire trucks meet us on the runway to verify that there was no fire. After we verified there was no fire we taxied back to the ramp and shut down the aircraft. Lavatory fires or indications are handled by flight attendants; we did not have any on board so we treated this like a regular fire and returned to field in a safe and efficient manner.The Captain's workload was extremely busy; my recommendation/lesson learned is to help the Captain out sooner in any way possible including helping by offering to take flight controls and lessen the Captains workload. Another recommendation is having a procedure for pilots in the event of [lavatory] fire for pilots when no flight attendants are on board.
Q400 First Officer reported the Lavatory Smoke alarm activated after takeoff resulting in a return to the departure airport.