A wearable apparatus is provided for capturing and processing images from an environment of a user. In one implementation, a wearable apparatus includes a transmitter, a memory, an image sensor configured to capture a stream of images from an environment of a user of the wearable apparatus, and a processing device. The processing device is programmed to receive the stream of images from the image sensor, analyze the stream of images to detect the external device in the environment of the user, and cause the transmitter to transmit an interrogation signal that is configured to cause a change in an aspect of the external device. The processing device is further programmed to analyze the stream of images to detect the change in the aspect of the external device and, after detection of the change, store in the memory information relating to the external device.