BACKGROUND Intraoperative awareness with explicit recall is a potentially devastating complication of surgery that has been attributed to low anaesthetic concentrations in the vast majority of cases. Past studies have proposed the determination of an adequate dose for general anaesthetics that could be used to alert providers of potentially insufficient anaesthesia. However, there have been no systematic analyses of appropriate thresholds to develop population-based alerting algorithms for preventing intraoperative awareness. OBJECTIVE To identify a threshold for intraoperative alerting that could be applied for the prevention of awareness with explicit recall. DESIGN Secondary analysis of a randomised controlled trial (Michigan Awareness Control Study). SETTING Three hospitals at a tertiary care centre in the USA. PATIENTS Unselected patients presenting for surgery under general anaesthesia. INTERVENTIONS Alerts based on end-tidal anaesthetic concentration or bispectral index values. MAIN OUTCOME MEASURES Using case and outcomes data from the primary study, end-tidal anaesthetic concentration and bispectral index values were analysed using Youden's index and c-statistics derived from a receiver operating characteristic curve to determine a specific alerting threshold for the prevention of awareness. RESULTS No single population-based threshold that maximises sensitivity and specificity could be identified for the prevention of intraoperative awareness, using either anaesthetic concentration or bispectral index values. The c-statistic for anaesthetic concentration was 0.431 ± 0.046, and 0.491 ± 0.056 for bispectral index values. CONCLUSION We could not derive a single population-based alerting threshold for the prevention of intraoperative awareness using either anaesthetic concentration or bispectral index values. These data indicate a need to move towards individualised alerting strategies in the prevention of intraoperative awareness. TRIAL REGISTRATION Primary trial registration (Michigan Awareness Control Study) ClinicalTrials.gov identifier: NCT00689091.