The purpose of a smoke detector is to detect smoke from a fire. If it fails to work, a house may catch on fire. If one house catches fire, it may spread to the neighboring houses.

The dead batteries don’t start the fire but they may prevent the smoke from being detected.

Chirping detectors need to be have the batteries replaced because the battery is low. Non-chirping detectors do not not to need to have the battery replaced. The batteries are designed to last 5 years. Why would you replace a non-chirping detector battery every year if it is not low on power?

Have your teeth cleaned every six months whether you have a problem or not. Have your oil changed every 5,000 miles whether it is showing signs of being old or not. Replace your furnace filter every three months whether it looks dirty or not. Change the batteries in your smoke alarm every year whether they are chirping or not.

Preventive maintenance costs a bit but saves even more.

Is every year more often than necessary? Probably is, but is easy to remember and doesn't cost that much.

I didn't say it cost nothing. Even without the data you want, you appear to be a smart enough guy to figure out it's a worthwhile program.

What data can't show is how more calls for service would result from old people on ladders falling, house fires where the occupants don't evacuate quickly (old popple move slower).

Bottom line it's a good service, embrace that. Same as going to schools and community groups for safety education - no data will show the net result. I bet you do know Stop, drop and roll, same as millions of others. Do you doubt that educational program isn't worthy?