Detecting and locating changes in a waveguide can be extremely difficult. A method is suggested here which does not require simplification of the problem (no spherical chickens) nor any modeling of the waveguide nor of the propagation within it. The method relies only on previous broadband data recorded on an array of receivers (two or more) which is then compared to more recent data to investigate change. Backscattered energy is to be examined here although bistatic configurations may also be possible. This approach is applicable whenever there is sufficient, appropriate data for comparison (note that absolute levels are not needed) and can be applied to acoustically search for scatterers introduced to an ocean zone (such as targets or pollutants), blockages or changes in sewer pipes, or even to non-acoustic energy in a waveguide, e.g., the use of electromagnetic energy in the earth-ionosphere waveguide. This method is based on the signal processing technique known as matched field processing and will be demonstrated on a variety of laboratory sewer pipe data. The method (particularly for localization) is introduced here, as is the suggestion for application to general waveguide environments.