Leon Theremin is alleged to have designed a spy device called “the thing”. Develop your own version of this device in such a way that you can maximize the ratio of its working distance to its largest linear dimension. The optimization should be made after choosing some working frequency less than 1 GHz and some transmitter power less than 1 W (see https://en.wikipedia.org/wiki/The_Thing_(listening_device) ). Take into account the legal restrictions on radio transmitters in your country!