Did I need a 'smart' smoke alarm? No. Did I see this and then try to justify it? Yes.Nest seems to almost create markets for things we don't really need. But these products are very well made, designed and thought out. Our carbon monoxide monitor had expired, so I took the opportunity to purchase this after reading some reviews claiming the sensors it uses are really good. I wanted something reliable I could mount and not worry about and this certainly seems to be the perfect candidate.In the box, you'll get a user guide, the Nest Protect, a mounting plate and some screws. It's as simple as you'd expect and takes about 15 mins to install. The unit itself feels very sturdy and well made and is quite nice to look at.Fitting - I opted for the battery model as the Nest will let you know once batteries are running low, and I don't have the wiring for a wired model in place. I was mounting this on a plasterboard ceiling so personally, I didn't feel the screws alone offered enough stability. I'd recommend fitting with some wall plugs if you have a plasterboard ceiling too. 6mm wall plugs (red) will offer a nice snug fit. Note that the Nest Protect can be rotated on it's base to lock it in, so you don't have to get the base mounted perfectly straight. It's also worth noting that it's a pretty big device, so should cover up any screw holes from a previous fire alarm nicely.Setup - Just download the app, create an account and scan the barcode/enter the serial. It'll carry out a test and then it's good to go. The alarm is much louer than my previous fire alarm which gives you the confidence of it being clearly heard.App - The Nest app is nice and clean and as expected, allows you to control the settings of your Protect. It has a log of when it has carried out checks, been activated etc. The protect also has a nice little light that is automatically triggered on it too which is perfect for hallways and landings at night. You can control the strength of the light via the app (min/med/max). As it's LED I don't suspect it'll reduce battery life dramatically. On the app home screen, you get a nice green indicator to show all is OK. You can also use the app to schedule the monthly check the alarm runs itself. It's a shame you can't fine tune the time (it offers windows such as 7am - 11am), but it's a reassuring feature. As is the fact that you can be notified if the alarm goes off remotely which is the major selling point of this. One other feature I was really impressed to see was the option to have the Nest Protect turn off your heating if it detects a CO leak. This only works if you have a Nest Thermostat and whilst it probably won't help much if there's a leak, it may offer some precious time. This is a clear example of how much thought goes into Nest products and integration.I can't comment on battery life and since it uses alkaline batteries, it can't monitor how much is left. I assume it will let you know when it is close to running out though. It's worth noting it uses long life batteries (included) so bear this in mind when replacing them.Overall, I'm very impressed by the device so far. My only reservation is the price, but when you factor Nest claim it ought to last 10 years, it's an investment. And the price covers Nest's costs to offer you that 10 years worth of updates, monitoring via their servers and support. It does feel overkill for what you need, but you've probably made your mind up about it if you've got this far!