In the nanoscale regime, the behavior of both extant and emerging semiconductor devices are often unreliable. Reliability of such devices often trades-off with their energy consumption, speed, and/or chip area. We study the reliability-energy limits for circuits designed using such devices; examples are drawn from spin electronics. Using the mutual information propagation in logic circuits technique developed by Pippenger, together with optimization, we obtain lower bounds on the energy consumption for computing n-input Boolean functions. We observe that the minimum energy requirement is strictly higher in an order sense (as n scales) than that in the case of reliable gates. © 2016 IEEE.