Smoke alarms are the battery or line voltage detectors that have a built in sounder - the alarm.
NFPA 72 2010 3.3.245 Single Station Alarm. A detector comprising an assembly
that incorporates a sensor, control components, and
an alarm notification appliance in one unit operated from a
power source either located in the unit or obtained at the
point of installation.
Smoke detectors are are the low voltage ones that only detect smoke. The "alarm" is a separate audible/visual that is activated by the fire alarm system.
NFPA 72 2010 3.3.59 Detector. A device suitable for connection to a circuit
that has a sensor that responds to a physical stimulus such as
heat or smoke.