An online system receives a request from a user of a manager transmitter to generate a unique beacon identifier (ID) associated with a physical location. Responsive to receiving the beacon ID from the online system, the manager transmitter transmits a Bluetooth signal comprising the beacon ID to user client devices, which send the beacon ID to the online system for identification. Responsive to detecting that a received signal strength exceeds a threshold, a location context module classifies the instance of the user client device detecting the signal as an example of a user being present at the physical location. A location prediction module uses the instance as training data to train a machine-learning model to predict the presence of online system users at the physical location.