circuit diagram for a fire alarm?

Answer 1

I assume by "fire alarm" you mean a smoke detector?
Here is a circuit diagram for a standalone alarm:
http://www.electronic-circuits-diagrams.com/alarmsimages/13.gif
Text that goes with it is on
http://www.electronic-circuits-diagrams.com/alarmsimages/alarmsckt13.shtml
If you want to integrate a sensor into your existing home automation system, then read this:
http://www.edcheung.com/automa/smoke_det.htm

Answer 2

It rather relies upon on the complexity of the equipment. all your detectors and activating switches must be under pressure so as that they are in many cases closed while the equipment is universal. That thank you to turn on the alarm, the circuit must be broken. it rather is performed for quite a few motives. First, if some thing damages between the loops, the equipment can sense there's a difficulty, rather than analyzing the priority while the equipment fails to artwork. Secondly, if the hearth have been to initiate in a community faraway from the sensor and burn in the process the wires, it would turn on the equipment, or a minimum of point out that there is a difficulty. in many cases, while a sensor or alarm pull is tripped, it switches from its low impedance state to a dazzling impedance state, activating the alarm. An open state is used to show a difficulty with the equipment, yet no longer unavoidably an activated alarm (although in many cases it quite is taken care of as such for protection motives). while you're doing this circuit for a demonstration, that's completely large. If it rather is meant for use as a real equipment, I quite advise which you look for a consultant provider on the subject of this, as what you will be able to finally end up construction will in all likelihood no longer meet hearth code. this might finally end up putting you in extreme legal legal accountability hassle ought to it malfunction.