http://avherald.com/h?article=4129ccf8

An Air Canada Embraer ERJ-175, registration C-FEJB performing flight AC-1043 from Toronto Pearson,ON (Canada) to Dallas Ft. Worth,TX (USA) with 72 people on board, was in the initial climb out of Toronto, when a smoke detector in a lavatory went off. The crew decided to return to Toronto for a safe landing.

Maintenance suspects that the smoke detector was triggered by fumes from residual detergent following a compressor wash of both engines earlier the day.