File:Cap’n Crunch bo'sun whistle (2600 Hz).jpg

A Cap'n Crunch bo'sun whistle, similar to one used by John Draper to generate a 2600 Hz tone to make free long distance calls.

Source

 * File:Cap’n Crunch, Spielzeugpfeife (2600 Hz).jpg by 1971markus. Wikimedia Commons. 2015-10-10.

Licensing

 * NOTE: The terms of the original uploader prohibit this image from being shared on social media.