The air flow around these areas could prevent the smoke-filled air from collecting in the detector in sufficient amounts as to activate it. Avoid installing a detector near bathrooms with showers. Steam can sometimes cause false alarms and the moisture can rust metal components of the detector. Also avoid areas where nominal amounts of smoke may normally be present, such as kitchens or other cooking spaces, furnace rooms, or near fireplaces or wood-burning stoves. More information on home installation.
Heat detectors are no substitute for smoke detectors.
They set off an alarm in response to heat only. They do add protection and can be helpful in basements, kitchens, attics and garages. But for life safety purposes be sure your home is protected by a smoke detector. Every detector comes with testing instructions. Activating the testing mechanism once a month should be sufficient.