Arduino Alarm using EPABX Intercom system.

Hi all, I need help in my New Project actually i need a Alarm system that do alarm when two things happens 1. is Smoke detection and 2. is Temperature. ok i have arduino uno and my planning is that i want to use my Intercom system that currently in use for calling to a predefined Telephone number when arduino gets triggered from temperature or smoke detector it automatic make call to a predefined telephone number can some one help me to point out the solution ? please give response to this .

Your project can be done in twenty small steps.
Step #1 : Understand your smoke detector.
Will the smoke detector have a wire soldered to it that has a voltage that is less than 5 volts?

Step #2
You need to finish step #1 first. This takes time, solder, voltage meters, and wire.
Maybe a wire not wanted. A microphone can be placed near the alarm to sense the loud siren. and send a microphone signal to an Arduino analog input.

Step #3 : tomorrow

Thanks for Great Idea Condenser mic can sense louder sound great .. i am waiting for next steps....

Where is Step #3 ??? pls help i am waiting for your reply /.... :~