  A CMOS-based implementation of an autonomous Maxwell's demon was recently
proposed (Phys. Rev. Lett. 129, 120602) to demonstrate that a Maxwell demon can
still work at macroscopic scales, provided that its power supply is scaled
appropriately. Here, we first provide a full analytical characterization of the
non-autonomous version of that model. We then study system-demon information
flows within generic autonomous bipartite setups displaying a macroscopic
limit. By doing so, we can study the thermodynamic efficiency of both the
measurement and the feedback process performed by the demon. We find that the
information flow is an intensive quantity and that, as a consequence, any
Maxwell's demon is bound to stop working above a finite scale if all parameters
but the scale are fixed. However, this can be prevented by appropriately
scaling the thermodynamic forces. These general results are applied to the
autonomous CMOS-based demon.
