Methods and apparatus for uniquely identifying wireless devices in close physical proximity are described. When two wireless devices are brought into close proximity, one of the devices displays an optical indicator, such as a light pattern. This device then sends messages to other devices which are within wireless range to cause them to use any light sensor to detect a signal. In an embodiment, the light sensor is a camera and the detected signal is an image captured by the camera. Each device then sends data identifying what was detected back to the device displaying the pattern. By analyzing this data, the first device can determine which other device detected the indicator that it displayed and therefore determine that this device is in close physical proximity to it. In an example, the first device is an interactive surface arranged to identify the wireless addresses of devices which are placed on the surface.