Google doesn't recommend installing Nest Protect in a garage. As they are usually not heated or cooled, the temperatures experienced in a garage may go above or below the temperature range that the alarm has been designed for. The smoke from engine exhaust fumes can also cause nuisance alarms and damage the sensors of the smoke alarm.
What does Google suggest to anybody that wants to install their Nest Protect products in a new home application where there is an attached garage or living space above the garage. Code in MA requires a heat detector interconnected to the system according to our electrician which both they and Google say is not possible.
This seems to be a very big oversight from the Nest Protect line of products if in fact this is not possible. That would mean anyone building a new home would not be able to install Nest Protect products (if they have an attached garage or living space above garage)