i would imagine typing 'smoke alarm design' into google would have some good results. or go to https://www.howstuffworks.com/ and search smoke alarms.
um, from my own knowledge, i can tell you that they have a radioactive material, that emits radiation (alpha, i think) to a collector, which measures the amount of radiation received. As smoke passes between the emitter and collector, some of the radiation gets absorbed, and so not as much passes to the receiver. this change is detected, and triggers and alarm.
so most of a smoke alarm is a simple sensor triggered alarm. its the radioactive emitter/receiver that is the tricky bit.
thanks for you help, i was asking this becuase i plan for a project to intergrate wireless links between, simple cheap detectors so that they all go off when just 1 is triggered. this would be cheap and remove any need to hard wire an alarm system.
does anyone have any detail on the sensors, eg is it just a logic 1 or 0 output?
does anyone know of any IC's/circut designs that would be best suited to the wireless communication, correct me if i am wrong but could i use a pic microprocessor to transmit a frequency, and also use is to detect a frequency, then use one of the outputs to trigger the alarm system?
or would there be a better way of implementing this?