With the access panel puzzle, once you've put in your solution you need to keep pressing down until the little enter button on the bottom is highlighted (that lets you enter your solution, it will tell you if it's denied or not). I'll update the walkthrough to say that.
Yeah, it's probably not the most well thought out puzzle, maybe something like a hearing device (stethoscope?) might have been better. I was thinking of those old cartoons where the character uses a glass cup to hear whats on the other side.
Thanks for checking it out though!