Walk to the fire alarm that is making the noise.
Find the "Silencer" or "hush" button on the device.
Press the button firmly with your index finger. It should silence immediately. If not, continue to depress the button until it shuts off. This silences the alarm for only a short period. If the smoke, steam or humidity remains in the air, it will sound again.
Ventilate the area if there is a kitchen fire or high humidity from a bathroom that causes the alarm to sound. Raise windows, open doors and use a ceiling or other fan to clear the air. Otherwise you may have to return and press the button again if it goes off a second or third time. Many fire alarms are sensitive and it will continue to sound until the smoke or other conditions clear.