A proximity detector miming on a server receives a request from an origin device to identify a proximity history of the origin device with one or more target devices and retrieves context information from the origin device and from the target devices. The proximity detector compares the context information from the origin device to the context information from the target devices that is within a time threshold of the context information from the origin device and generates a list of a subset of the target devices that satisfy a proximity threshold with respect to the origin device based on comparing the context information that is within the time threshold. The proximity detector generates an ordered list of events, each event indicating when a target device satisfies the time threshold and the proximity threshold with respect to the origin device, and provides the ordered list of events to the origin device.