The Tyco MF901M is an Ionization chamber Smoke Detector (516.051.001), and is part of the M900 Series of Analogue Addressable Fire Detectors.
The Tyco MF901M can be plugged into an M600/M900 Universal Base to form an analogue addressable Detector. The MF901M is designed to transmit an analogue signal, which represents the state of the sensing chamber.