I always thought those devices looked a bit creepy:

"The Truth About Wireless Devices" - http://www.wellingtongrey.net/miscellanea/archive/2007-05-27--the-truth-about-wireless-devices.html

---

Updated 2021 : note that the above post is out of date as it was originally published in 2007, but is left here for archival purposes. The external link is now dead so I have unlinked it.