I've written a tutorial for Gamedev Tutsplus.
Here is the teaser for the article :
Doors play an essential part in the navigation and progress of the player in many game genres, and locks that require keys are the perfect way to control the flow of play. In this tutorial, we'll examine the basic logic behind doors, locks, and keys.
All of the examples that illustrate the article are made in Construct2 and the capx files are commented and can be downloaded from the article.
(The "Download attachment" button on the right side of the article)
Notice it is aimed at intermediate users, but hopefully, beginners can find it useful to a certain extent. Nevertheless it's not a "follow the recipe" kind of article.
I hope you can find this article and the examples useful.