Why don't they build in a simple fail safe on the Nest? That is, have a user settable manual switch that fails to "heat on" if there is no response from the ma

Why don't they build in a simple fail safe on the Nest? That is, have a user settable manual switch that fails to "heat on" if there is no response from the main unit. The house would be quite hot - but probably much less damaging than frozen pipes. The liability costs for frozen pipes could be staggering.