[unixfox]

...and the discovery of a wireless transmitter that seemed to be carefully hidden in the gravel under some tracks in Philadelphia.

A transmitter could be anything from a garage door opener to a cell phone. The RECEIVER is what I would be worried about.

[AFPhys]

If you did not look at the rest of the thread, it might be a good idea to. There are several proposals for how to use a transmitter included by freepers.