Mini Object Lesson: The Smoke Alarm Chirps at Night

Flickr/Katy Warner

Ever wonder why smoke alarms always seem to chirp in the middle of the night? It seems like the ultimate evidence that the universe is plotting against you. But, alas, it’s mostly just the universe chugging along as usual.

The residential electric grid is subject to voltage fluctuations. This is caused by many factors, including local area usage, but it can also be driven by planned operational changes in power-generating plants and equipment. Various factors can introduce voltage fluctuations, including surges from storms, large nearby loads, resistance in transformers on a transmission line, or a home’s location on that transmission line. But generally speaking, the demand for power is lowest at night, when most users are sleeping rather than running microwaves and washing machines. The reduced current demand causes a subsequent reduction in power transmission loss, which can result in higher voltage higher along a transmission line.

Meanwhile, smoke alarms are fairly sensitive pieces of equipment, responding to voltage fluctuations more readily than other electrical infrastructure. Many homeowners assume that a chirping smoke alarm always means a low battery signal. But often, night chirping occurs when the whole apparatus encounters some unknown electrical fault. It might indeed be the battery (and loose voltage helps hasten its demise), but it is just as likely that the device got confused from a fluctuation or surge and thinks it’s experienced a line-fault, at which point it also detects a low battery, and/or the need for be reset (ugh, seriously, check the manual) and/or that it needs to be replaced from having been fried by the surge. I know, I know, we can put a man on the moon, but …

Smoke alarms alert their owners of possible catastrophe. And for that reason, manufacturers don’t necessarily mind if the devices cry wolf a bit. In fact, smoke alarms are more like puppies than they are like air conditioning condensers. They require a great deal of care, most of which homeowners never provide. Few test their smoke alarms monthly as recommended. And if you read the fine print, you’re even supposed to clean them with compressed air regularly to remove dust. Even a rogue insect crawling around inside one can cause a false alarm or damage the circuitry (this happened to me once).

‪A whole-house surge protector installed on the main electrical box can filter out over-voltages from the utility line for your residence, but it costs a few hundred dollars, and it might not help anyway—although at 3 a.m., any price might seem worth paying to stop the night chirps, even if hypothetically. But one small, cheap, and easy thing you can do, night chirps or no: change your detector batteries when Daylight Savings starts and ends—at least then you won’t have to wonder if it’s a dying battery waking you up at night—let alone a real fire.

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