Find Information On This Component Of Fire Alarm
With the IC part number, I was able to find this for you:
http://pdf1.alldatasheet.com/datasheet-pdf/view/218677/SENSITRON/A5366CA-T.html

The "typical application diagram" should be able to help you considerably, even if I am not.

Pin 7 is I/O interconnect:
When driven high by the Arduino, the alarm will sound. When read by the Arduino, a HIGH signal indicates the alarm is going off.

Pin 11 is LED output and flashes to indicate the current status:
Standby - Every 43s
Local Smoke - Every 0.5s
Remote Alarm - No pulses
Test Mode - Every 0.5s
Timer Mode - Every 10s  

You should certainly be able to detect those with an Arduino.