The use of utility bills to benchmark building performance is a critical first step in any approach to energy conservation. However, utility bills can only tell you so much about how to improve building performance. Five multifamily buildings received circuit level electricity, temperature, and CO2 monitoring equipment. The data identified inefficient mechanical designs, incorrect installations, poor maintenance and individual apartments with high energy use. We will review what we measured and what we learned, including energy savings as a result of this monitoring strategy.