In certain areas of the behavioral sciences, such as cognitive and perceptual psychology, researchers may choose to have their experiments partially or completely driven by software programs, which instruct and guide subjects through the sequence of tasks. Despite distinct advantages of unattended trial execution, on frequent occasions, experimenters may desire to keep track of the progress or to be notified of certain events, such as when the subject has completed a task. The Tracer software library presented here is a lightweight Windows programming interface that provides experimenters the ability to trace events and status notifications on one or more remote computers and log files. With only a few lines of additional code or script code, researchers can monitor the real-time progress of one or more unattended experiments running on remote computers of the local area network or the Internet. This article describes the functionality and usage of the Tracer library. The Tracer binaries, include files, sample code, and documentation files may be downloaded from the Psychonomic Society Archive of Norms, Stimuli, and Data at www.psychonomic.org/archive.