Unlock is a unique little puzzle game in which you must unlock the secrets of each stage to advance to the next. Some stages are easy, while others are maddening difficult. This game will tease your brain and test your patience and resolve.
Another game designed by Uminin of Flash Game Zone in Japan. And while it's definitely a smaller scale Flash game than his more recent offerings, this game offers a variety of puzzles to keep you interested, and to keep you guessing. He first created "normal" mode, and then added "another security mode" a month later. Together they form 12 challenges for you to unlock. Click.
This game reminded me a lot of Jonathan May's The Dark Room, though on a smaller scale. If you like games like this, then check out Jonathan's excellent puzzler, too.