It's not recommended to put a smoke detector in the garage, the exhaust fumes may trigger a false alarm. Since its' a 3 car garage, you might be able to place one so that false alarms are minimized. The wireless ones may be a good idea.
Heat detectors are usually placed in garages for that reason. I would also suggest a multi-gas detector, capable of detecting Natural Gas, Propane, and CO:
http://www.firstalert.com/carbon_monoxide_alarms_item.php?pid=26
Vin