Here’s one from the “why the HELL didn’t anyone think of this before?” department. It’s a Dupont smoke alarm (US$33.95) that a lightbulb screws into. The battery on the detector charges when the light is being powered. When fully charged, the detector can allegedly work for 30 days without the need of recharging. I’ve seen emergency flashlights that charge this way, but never detectors. I don’t know about you, but I HATE changing the 9V batteries on screechy smoke alarms.