If the Nest does not recognize movement after awhile it will set to Away. Which is a great feature to have since I don't have a set schedule. I also love the ability to control it through my phone.
The Nest does have a lock feature so that it can't be accessed without a code.
The fact that it changes if it doesn't recognize movement is exactly why it is of no use to me. I may be in the basement or another room for hours...it won't recognize movement, but I'm still home and want the temp to remain as set. My schedule is also erratic, so I simply set the programmable to "hold" or change program to start before my planned arrival.
I don't like wasting fuel if I'm not home, so I NEVER forget to adjust the program if required. A nest would "wait" for a predetermined time before making the change, or use a "learned" schedule that may not be accurate...both of which will waste fuel or electricity.