Rechargeable Smoke Detector

Apparently sometime during the 1970's, somebody associated with Honeywell Inc. had this patent-worthy idea. Now, thirty years later, installed versions of similar rechargeable smoke detector devices seem to be remarkably scarce in residential applications.

Rechargeable battery backup power source for an ionization smoke detector device

United States Patent 4155081

A circuit for a rechargeable battery backup power source used with an ionization smoke detector device whereby upon the failure of the main alternating current power source, a battery which is normally charged from the power source during standby operation is connected to an ionization smoke detector circuit to maintain its energization upon the loss of the alternating current power source.

Read more: freepatentsonline.com

Just curious: How many non-rechargeable 9 volt batteries do well maintained residential smoke detectors "consume" during their functional life-spans in homes built in conformance with current building codes

??