This paper describes an experimental study of workers' responses to proximity warnings of static safety hazards on construction sites using a location-based proximity warning system named the Proactive Construction Management System (PCMS). A method of evaluating workers' responses to proximity warnings is proposed. The method consists of six variables: warning time and distance (the time and the minimum distance to a hazard when a worker receives a warning), dangerous time and distance (the time and the minimum distance to the hazard when the worker comes close to the hazard), and response time and distance (the difference between dangerous time and warning time, and the difference between dangerous distance and warning distance). Finally, whether a worker responds to a warning is evaluated against a two-second threshold and a two-meter threshold in terms of response time and distance respectively. The experiment was conducted over 17 workdays with the participation of 72 workers and resulted in 5391 warnings on a real-life construction project in Shanghai, China. The workers' responses were analyzed with respect to two factors: building trades and a-priori risk levels. The research found that workers responded to proximity warnings actively, but slightly differently across the selected building trades; carpenters had longer response latency in hazardous areas than ironworkers did, and response percentages were high for hazardous areas with high risks. The results also show evidence that PCMS has the potential to improve workers' safety performance. The limitations of the present study and future research directions are also addressed. (C) 2016 Elsevier Ltd. All rights reserved.