The firefighter wired smoke alarm is for the monitoring of your local 120v Interconnected smoke alarms, and runs about $57.
You can get them here, and here
Personally, I am on the fence about this as some may depend on it to sound an alarm in the event of a fire to the exclusion of photo/heat detectors (most home 120v interconnected smoke alarms are ion detectors (flaming fires), and poor at detecting the most common home fires which are smoldering fires).
In a smoldering fire your home fills up with dense smoke, and if sleeping, you become overcome, and rendered unconscious and unable to wake.
Most who die in home fires, die because of the smoke. In a home fire, your window to successfully escape is short, and Ion smoke alarms can take up to 40 minutes to sound the alarm. (Fire Marshals recommend a home have BOTH photo/heat and ion detectors installed to maximize detection, and provide an early enough warning to successfully escape the fire)
And that is where IMO, the Firefighter comes into play.
Ideally, the benefit of using this is say you have monitored photo/heats, AND 120v interconnected ion smoke alarms... Use this to have the panel monitor the ions. That way whether asleep, or away, your panel will sound the fire alarm, and help will be on the way regardless of whether it is a flaming fire or smoldering fire.
Always test your smoke detectors and smoke alarms at least annually preferably using canned test smoke.