If you are trying to detect smoke as an experiment (and NOT to protect your house), you can have fun with this circuit.
A simple smoke or particulate sensor can be made from a pair of simple Red OR Green OR Blue LEDs (do not use white LEDs).
One LED is simply wired with a resistor in series to give off Light. The other is placed 90° to the first and is wired like a photoDiode and used as a sensor.
Put each LEd in a Shroud - like an old 35mm film canister, a prescription pill bottle painted black or the shaft of a black-body from a bic (or similar) ball point pen. Then position the, at 90° to each other so when the red light of the LED hits the smoke, the smoke can be be reflected into the second LEd. It is best to use the T1 3/4 (5mm bullet) indicator style LEDs.
Something like the following for a very basic proof of concept.
Then you can move on to use a modulated LED light source (e.g. 38kHz) and a filtered detector to cancel out ambient light.
Have fun. Don't use this circuit as a life-saving device. Also, it doesn't work well for black smoke (soot/lamp black) but works well on smoke from wood or paper fires - including cigarettes.