I need some information about how to detect someone using ultrasonic fequencies to harrass (crossing them to create a phantom loud speaker). Someone has suggested using a transducer – used in old us tv remote controls – an amplifier, a tunable oscillator operating at us frequencies, a detector (like used in an am radio) another amplifier (for audio) and a speaker and headphones. Are they having me on? Would this work? Is there anything else that will detect, trace, and stop this? What kinds of equipment can produce these frequencies? Am I looking for something close-by? Across what kind of distance can they operate?