From Michael Weinberg of OSHWA on OpenSource.com:
Check out these unique conference badges that attendees can take home and play with.
In the beginning, there were conferences. Over time, as those conferences grew, attendees needed ways to identify each other. This need gave us the conference badge.
No one knows what the first conference badges looked like, but we can be confident that they were relatively simple affairs. Over time, paper was put into plastic sleeves, which eventually became information printed on hard plastic. Sometimes that plastic wasn’t even rectangular.
At some point, batteries were introduced, and then things started to get a bit crazy. Today, many conference badges are intensely elaborate affairs. Some of the best of them are also certified open source hardware.