Why is my front room ceiling fan switch setting off my smoke alarms
There are two types of smoke detectors, Ionization and photoelectric. If you have the latter, it might be that they have some particulate around the photocell and when the fan goes off it disturbs the dust enough to simulate smoke. If you know your type and manufacturer you can check your manual (many are online) and follow the cleaning procedures. 

If you don't know the manufacturer sometimes you can bag the smoke detectors with a "shower cap" or a plastic bag and a rubber band and see if turning on the fans will set of the alarm. 

After that it gets a little complicated and you might need to consult an alarm specialist in your area.

Good luck.