An interesting use of energy is in "The Thing" which is powered remotely and acts as a listener-transmitter.<p><a href="https://en.wikipedia.org/wiki/The_Thing_(listening_device)" rel="nofollow">https://en.wikipedia.org/wiki/The_Thing_(listening_device)</a><p>"The existence of the bug was discovered accidentally in 1951 by a British radio operator at the British embassy who overheard American conversations on an open radio Soviet air force radio traffic channel as the Soviets were beaming radio waves at the ambassador's office.[9] An American State Department employee was then able to reproduce the results using an untuned wideband receiver with a simple diode detector/demodulator..."