Technologies for allowing people or other entities to detect others with common interests, particularly when proximate to one another. A user can configure a mobile device with information about his interests, such as things they wish to buy or sell, the kinds of people they would like to meet, or any other interests. Such a mobile device may federate with other similarly-enabled devices such that interest information is exchanged and interest matches are sought. Such exchanges and/or matching may be limited by physical or geographic proximity, such as when two people are physically close to one another. Upon discovery of a match, the user is typically notified of the match and the user's contact information may be forwarded to the other matching user's device.