FYI the 79DCRI smoke detector:
This detector is used for Operating a Solenoid that will drop a louver in a ventilation system.
When the 9 volt powered Smoke Detector goes off it sends 2-3 amps of power to a solenoid that heats up enough to melt solder. There is a soldered clip on the solenoid that is released when the solder heats up when the clip drops the louver falls shut by gravity.
When this unit goes off you have to solder the clip back on the solenoid to operate the louver once again.
The louver acts as a ground to complete the circuit. thats how it works and that is why there are extra wires on the smoke detector.
Kind of cool a 9 volt battery can power this up but it works well.