On the FO NT, Amada added lens fire detect sensor. It's a cool idea but doesn't always work the best.
On top of the gantry, behind the Z axis motor, there is a little Keyance sensor. It has two fiber optic wires coming out of it. One sends light to a spot right above the focus lens and the other picks up the light that is reflected off the inside of the cutting head. When the lens catches fire, the smoke instructs the light path the keyance sensor detects the change in the light level and triggers the alarm you are having. I think.
There are two big problems with this system. One, the fiber optic cable gets old and the amount of light transmitted and received changes. This causes false alarms. The other problem is the plasma generated when cutting heavy stainless or aluminum. The light is so intence that is over rides the light generated by the keyance unit and again, causes a false alarm.
The good news is the light sensing levels can be adjusted to compensate for the false readings. The bad news is if you adjust the thresholds out too much the unit will ignore a real fire.
If you want, I can post a proceedure for adjusting the Keyance light sensor. I worry that if I do, someone is going to screw up three machine and blame me.