All fire alarm boxes have unique identification numbers. When the white lever is pulled, it sends an alarm to the Fire Alarm Office with the number of the box. The emergency responders who receive the alarm then look up the address of the box and send the closest available fire trucks to the spot.
In December of 2018, the 911 system in Boston went down for a day due to a computer glitch. While police and medical personnel relied on using lesser known 10 digit numbers for incoming emergencies, the fire department just told citizens to use the fire boxes. They came in useful during the downtime, when a fire broke out in a laundromat in the North End and a resourceful citizen pulled the fire alarm!
See them on many of our Group Boston Tours!