A new extremely effective method of finding strong alternating codes for incoherent scatter radars has been invented. The power of this method is described by the fact that the longest code known at the moment contains 4,194,304 bits, whereas the older methods could find codes only up to the length of 32 bits. This result means that strong alternating codes are now available for all needs of any present or future incoherent scatter hardware which one can imagine. The search method can be explained in two ways. The first one is an astonishing game of dominoes, which is not useful in the practical search but allows the search method to be easily visualized. The second presentation is a mathematical description of the method in a form suitable for computer search. The method is explained in a series of two papers. In this first paper the presentation of alternating codes in terms of Walsh indices is reviewed and the game of dominoes is described. The second paper gives the underlying mathematical formalism as well as several long codes in terms of their Walsh sequences. ¿ 1997 American Geophysical Union