A few years back, I did a stint as a visiting professor at Harvard.
Various communal rooms on the uni campus had detectors which were sensitive to UV light. I think their correct name is UV optical flame detectors.
These detectors would pick up someone merely striking a match in the room, resulting in the activation of the central alarm network. Furthermore, they were so sensitive that they would detect the glowing end of a cigarette even if the cigarette had been lit outside the room. Believe me, they were a right pain in the neck especially since I don't smoke myself.
The ionisation chamber and optical types we use in UK are far better in my view.