Installation is relatively easy: it simply requires the application nest on an Apple or Android device; scan the code on the detector used to configure it simply, then just follow the steps in the application. Once set, the sensor can be fixed.
The Nest supports a ceiling installation (recommended) or wall. To know that, like any sensor, the installation must comply with constraints specified in the manual: not too close to a wall, a neon, etc. It detects smoke and carbon monoxide. It has a function to prevent false alarms due to water vapor (eg hot shower ...) and despite the proximity of the bathroom, it actually seems to work well.
The interesting features of this model: first he announces the status or problems clearly, indicating eg the place or the room where the smoke is detected (of course it also sounds, loud enough to wake up ...) . Then the detectors can be interconnected: if you have multiple detectors, all detectors in the house will ring when one detects smoke, and they will indicate where the problem lies. A message will also be sent via the Nest application (on the phone or tablet).
He then has some additional features (activated or not in the application): nightlight that lights up the night when passing (although it works less well when the sensor is on a wall), peaceful night (it glows green lights out to indicate that all is well. The application allows to check its status and distance history.
In the end, a simple sensor to use, modern and rather design. Main complaint, the price a little high though. Especially, it should be noted that the life of the sensor before the change is indicated to 7 years.