In addition to its psychological definition, the Gaydar is also the name of a small, keychain-sized electronic device produced by the Toronto-based company Gaydar Direct.

At about 2.5" x 1.5", it is about the size of a car remote, and is designed to send out radio signals to other similar devices. The device, obviously, is designed to be worn by homosexuals, who wish to identify and meet others of the same sexual orientation while preventing potentially awkward situations before they occur. When the Gaydar comes within about 20 feet of another activitated device, it vibrates quietly, letting its user know that another of the same orientation is nearby.

The device sells for about $70 each. More information is available here, which appears to be the product's official website: