On your phone you can set your device to an away temperature and your nest will set to that temperature when your phome is out of range. If you dont have it set up for home or away you and set your nest to whatever temperature you want. The home away function is awesome when i get home the heat kicks in and it is great to walk into a warm house. I dont think it will alert you of power failure not positive but if you check the app while you're away it will tell you if its offline or it will tell you what temperature its set at. Yes there is an app for nest for your smart phone. I think it's great. Hope that answers your question sorry for the delay.