Smoke detectors are generally used in advanced alarm systems. Most of this professional devices use gas-detectors, ionization rooms or radioactive elements as sensors. In this circuit we are not using any of this complicated components.
http://www.circuit-projects.com/miscellaneous-circuits/ldr-a-led-pair-smoke-detector-and-alarm-by-lm1801.html
This circuit uses a very simple approach to detecting smoke in the air. Quite simply, it uses a bulb as a light source, and an LDR (Light Dependent Resistor) as a light detector. As fire smoke comes between the bulb and LDR, the resistance of the LDR changes, which in turn trigger an alarm.
http://www.electrokits.com/Security/Fire-Alarm-Smoke-Detector
I have always wanted to alert the Home Automation System if the smoke detectors were triggered. I had previously thought of using a microphone near one of the units to pick up the sound of the siren, but this seemed a little kludgy to me.
http://www.edcheung.com/automa/smoke_det.htm
Smoke Detectors are designed for 3 basic types of system implementations, Standalone, Wireless Connectivity, and Fixed or Wired Connectivity, the first two being battery powered implementations.
http://focus.ti.com/docs/solution/folders/print/334.html