It seems that most older aircraft have battery-powered smoke detectors in the lavatories, while most newer aircraft have hardwired ones. I presume this change was made to prevent tampering by removing the battery.
Does anyone know about when did hardwired smoke detectors in lavatories become standard? I know that in most U.S. homes, hardwired smoke detectors became standard in the early 1990s, however, most residential hardwired smoke detectors have battery backup. I don't think the smoke detectors on most newer aircraft have a battery at all.
[Edited 2013-07-10 14:09:50]