Wastewater treatment systems employ upset early warning devices (UEWDs) to detect and to attempt to mitigate sudden changes in influent composition, changes that may arise from activities by upstream dischargers, wet weather flow, or recycle flows from within the treatment plant. This report examines a range of UEWDs currently employed, or in development, and evaluates them relative to the characteristics of an 'ideal' UEWD. It also recommends research directions for improving UEWDs and integrating them into automated wastewater management systems.