<a href="http://lucidscience.com/pro-basic%20spy%20transmitter-1.aspx" rel="nofollow">http://lucidscience.com/pro-basic%20spy%20transmitter-1.aspx</a><p>That takes me back.. that looks very similar to something I built out of an article in an electronics magazine article in ~1987.<p>I do remember it had remarkably good sound quality from such a simple circuit - it basically sounded like "professional" broadcast talk radio. Lots of fun spying on siblings etc.