Absent from many of the larger, often effusive, articles about the new Nest Protect smoke detector is the answer to what I think is a pretty big question: What happens when you have to replace the thing?

Like any other smoke detector/carbon monoxide alarm, the Nest has a product lifetime of roughly seven years, which is about how long it takes for the device’s internal sensors to naturally wear out. After this point, owners either have to replace the devices or hope that the now-ancient things don’t stop working when they’re supposed to.

While the Nest Protect is a lot more advanced than the average smoke alarm, not even it can escape this fate.

The difference, however, is that the average smoke detector/carbon monoxide alarm costs $30, while the Nest Protect runs for $129. This makes replacing the device — let alone several of them — a significant investment.

More interesting, perhaps, is what happens when that expiration day comes: The Protect will tell you. Here’s how Nest describes the expiration process in the Protect’s user manual:

About two weeks before it expires, Nest Protect will light up with a yellow light. Wave at Nest Protect and it will say, “Nest Protect has expired. Replace it now.” Buy a new alarm and recycle the expired one. Make sure you test your new Nest Protect once it’s installed.

But what happens if you try your luck and keep your Nest Protect running past the seven-year mark? “You’ll no longer be protected from smoke or CO if you don’t replace your Nest Protect,” Nest warns.

Of course, none of this is to say that the Nest Protect won’t cost substantially less in seven years, nor does it preclude Nest from offering some kind of trade-in program for replacements down the line.

Still, is the kind of thing to keep in mind when investing in a device like the Nest Protect, which, while impressive, costs real money to both buy and replace.

VentureBeat's mission is to be a digital town square for technical decision-makers to gain knowledge about transformative enterprise technology and transact. Discover our Briefings.