This document discusses legacy building management systems (BMS), Internet of Things (IoT)-enabled BMS, and combining the two. It provides examples of legacy BMS from companies like Siemens and Johnson Controls. IoT-enabled BMS integrate additional sensors to improve monitoring and control. Case studies show how adding IoT sensors to legacy BMS can optimize operations and energy use. The document also discusses faults that can be detected through integrated monitoring of legacy and IoT devices, like using CO2 sensors to detect abnormal HVAC usage.