ATM environment alarm system

• Green steady — all good
• Amber steady — warning threshold exceeded, filter relay on
• Amber flashing — sensor fault, readings unreliable
• Red steady — alarm threshold exceeded, relay on + audible
• Red flashing — alarm + sensor fault simultaneously, machine stop relay — "stop what you're doing"

The relay — good idea to start the extraction filter automatically at warning level. Ties nicely into inverse_output / hvilestrøm config already in place.
Sensor fault in CSV — rouge but workable as you say. A simple approach: use one of the spare fields in particle_t as a status byte: