Smoke alarms are generally not used in attics due to false alarms from heat and dust and rate of rise heats can not be used due to rapid temp movement when fan etc comes on must be a fixed heat detector 185 usauly or the more exspensive rate of compensation type heat.

Detectors should not be placed flat on roof but on underside of stud.

Have seen cases where heats have picked up a fire but usually well after fire dept has been called.

In case where wiring for the smokes in the bedroom cieling below attic space are installed and wiring is run thru attic have seen fire alarms activate when the wiring melted in attic if the fire in attic .

have seen plenty of battery smokes melted off cielings and walls but usually where in path of fire.