I've got a Nest smoke detector in my alarm, so I'm kind of out of the running here, but if you, like most the rest of the population who'd rather not have their house burn down, have a standard 9-volt battery-powered smoke detector, the Roost is an extremely compelling proposition.
Granted, at $35 ($65 for a two-pack), it's a heck of a lot pricier than the 9-volts your weird older cousin used to lick for kicks, but you're getting a lot for that price. For starters, the thing is lithium ion and promises five years of life, according to the company's estimates. Once that's done, the battery snaps off the end of the unit and can be replaced.
More to the point, though, like the Nest, the Roost (you catching the theme here?) connects to your home's wireless network, and through that to your smartphone. Once it's connected, the status can be monitored through a simple app, notifying you about smoke alerts and low-battery charges.
We'll be getting some real hands-on time with a Roost unit soon, so we'll report back (including whether or not my apartment burns down in the process). Or you can just order one online now for $35 a pop and try it yourself.