Battery powered smoke alarms have an annoying low battery mode. It emits a single short beep every few minutes to alert the user and not drain the battery completely before it is replaced. The problem is a single beep is very difficult to locate, especially when you have half a dozen detectors.
In addition to the beep, the detector should activate a small bistable indicator. A solenoid based or e-ink based pixel would consume zero power. The user would be able to glance at the detector and determine if it was the one beeping.
This would also be useful in hardwired linked detectors. During an alarm, the user would be able to quickly see which detector was tripped, and replace a finicky detector which keeps crying wolf.-- Aq_Bi, Jul 26 2011 How about a smoke detector that gives out smoke signals when it gets low batter?
Then you can either see it, or the other smoke detectors in the house will get set off, because of the smoke..-- not_morrison_rm, Jul 27 2011 A smoke detector that contains a small digital audio recorder so you can identify which room it's in instead of chasing the beep: "I'm the one in the guest bedroom! My battery's dying! Help!"-- Alterother, Jul 28 2011 Oh come on- that smoke detector should just spout out some smoke when the battery is low!~!-- xandram, Jul 28 2011 random, halfbakery