I was reading about a Unified electrical code thing enacted in 1999 that requires new homes or significant changes to incorporate arc fault circuit interrupters (AFCI) in your main circuit panel. They had an extra white wire that had to go to the correct grounding bus. Sound like a TING with teeth to shut off the power.
A few years later, there was an additional requirement for arc fault circuit interrupters in outlets in every room except bathroom. (reason something about nuisance tripping of breaker there).
Somewhere around here a requirement for lighting circuits to have these too.
If i remember right basements and other non-living areas might not have been included.
Someone was wondering why certain homes were selected to be monitored.
Perhaps it is these 25yr old dwellings might need a higher fire risk cost if they were not monitored some way. I know many of our ground fault outlets tested defective by the electrician although they seemed to work ok.
Incidentally i was looking at costs to update using a popular web based store and 20 amp AFCI breakers for our panels brand of breakers were $33 and 15 amp AFCI breakers $15. 220 volt AFCI breakers were many times higher. remember extra wire must be wired correctly.
re AFCI outlet think 15 amp was around $15. Unsure how many must be used on every line to meet codes and I am not an electrician but often acquire stuff for a licensed electrician to install for me. Assume they may need special wiring as well.