How do fire inspectors disable the audible fire alarm signals when testing the fire alarm system?

Hello everyone. I went to a school for the visually impaired in Maryland and I am very fascinated with fire safety systems. Twice a year, a technician from Simplex, the alarm monitoring company, would come to our school to conduct tests of the fire alarm system. Initially, I thought technicians activate a fire alarm pull station, which would sound the audible alert tone and strobe lights. However, our Simplex guy has been doing “silent tests”, where he uses a broom to spray fake smoke in the smoke detectors. This would send a signal to the fire alarm panel, but the alarms would not sound. 

How do inspectors do this? I didn’t think they could disable the alarms, and I’m very interested in the field of fire safety. How does this all work? Could someone please try to help me out? I would greatly appreciate it. Thank you.

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