Abstract: An electronic puzzle device, including: (a) an array of indicators, each of the indicators capable of alternately indicating a first state or a second state, the array having an axis, which may or may not be physically indicated, dividing the array into a first portion and a second portion, and the array being capable of being folded along the axis such that each of the indicators in the first portion is corresponding to one of the indicators in the second portion; (b) a selection input for choosing or detecting a direction of the fold along said axis; and (c) a changer for changing the state of each of the indicators in the second portion depending upon the state of corresponding indicators in the first portion.

Abstract: Reminder apparatus to be carried by a user with a key constructed to remind the user as to the last operation in which the key was used with respect to a lock. The key includes an operation sensor which stores the time of the last key operation, and a display which, upon manual operation of the key, displays the time of the last key operation.