Fire extinguisher classes?
I don't know, it might be a good idea to call the vet and ask.
3 ways. 1: the first contains a photoelectric cell that detects light refracted by smoke particles. when it senses enough of this light is it creates an electrical current that sets off a light. 2: Some are called ionization type and basically they have a small electrical current in them. Smoke particles attach themselves to oxygen and nitrogen ions, therefore decreasing the current flow which triggers an alarm. 3: some old planes have a duct that routes air to a sight gauge in the cockpit where the pilots can actually view the smoke in the glass. Thanks deepseteyes, its always good to get knowledge from a grizzled vet.
Same way as any other, but if you try to disable it, the operators know its been done and you are in a world of trouble. Sit back down and chew some gum!