I am doing a physics "how things work" project on a smoke detector, and I need to get in contact with an "expert" on them, who knows how they work, and the physics behind them. If someone could help me out.

Basically, they have a small alpha radiation source, a small air gap, and a radioactive detector.

The detector triggers if the counts/second measured at the detector is lower than a threshold amount.

If smoke passes through the airgap, all the particles in the smoke absorbs and scatters some of the alpha particles, meaning that the detector drops below the threshold level, and the alarm sounds.

Is there no other way to do this cheaper? Like... a photogate system or something?

I don't know... maybe that would not be cheaper.

The radiation detector is in fact cheaper than an optical sensor. It can also detect smoke particles that are too small to attenuate light.

All the radtiation detector needs is a radioactive source, and 2 electrodes.