Hi Bob,
Smoke detectors are not used in unfinished attics. They need to be in a controlled environment where extreme heat, cold, humidity and (most important) dust are minimized. The usual approach is to install rate-of-rise heat sensors in the attic. These are only to be used as accessories to a fire or combined fire/burglar alarm system. They are *not* life safety devices though.
BTW, there is one System Sensor (brand we sell online) smoke detector that is designed for dusty environments. It wouldn't be appropriate for an attic though, due to heat limitations and frequent service it requires. I mention it because it may be of interest for other difficult locations. Following is the spec:
System Sensor FTX-P1 Filtrex Intelligent Photoelectric Smoke Detector System Sensor Filtrex Smoke Detector provides early warning smoke detection in difficult environments where traditional smoke detectors are not practical. Filtrex provides protection in dirty, dusty environments that tend to cause false alarms with standard smoke detectors.
Operation: Using a small air intake fan and a high density replaceable filter, air and smoke are drawn into a photoelectric sensing chamber while airborne particulate and water spray are removed. When the filter becomes too clogged to draw adequate air into the sensing chamber, power is cut from the detector, causing a trouble signal at the fire alarm control panel. When the filter is replaced, power-up is automatic.
Features:
a.. Intelligent communications b.. High density filter removes particulate down to 32 microns c.. Air delivery system is separately powered and fully supervised d.. Filter is easily field replaceable e.. Resistant to water spray in applications where occasional hose-down cleaning is performed f.. Optional remote LED accessory g.. Rotary decade address switches h.. Compatible with 200 and 500 Series products' protocol i.. No modification required to panels compatible with System Sensor intelligent photoelectric smoke detectors Applications: a.. Animal research facilities b.. Institutional laundry facilities c.. Amusement parks d.. Zoos a.. Performance theatres b.. Loading docks c.. Paper mills d.. Textile mills