If its an old installation, check the detector head and housing for excessive dust. Detectors can be blown out with compressed air or replacement detector heads ordered, 55000-328 for -P model or 55000-225 for the -N model.
If detector is interconnected to another detector in the system, this can be checked by looking to see if there are wires on terminals 12 and 20, check to see if the other detector is maybe in alarm.
If its a new installation, if detector has been wired to a remote or accessories remove wiring such that only power is connected, if it stops going into alarm confirm correct wiring for model of remote when reattaching and that key switch is not activated.
In some situations of high humidity or temperature swings such as in sunbelt states condensation can build up on and inside detectors which can cause false alarms, we recommend moving a detector further downstream on ductwork or inside building where temperature swings might not be as extreme.
If detector still goes into alarm when all wiring removed, replace detector head or RMA unit.