Ah yes, the dark. Turns out I was the only adult capable of investigating why the safe wouldn't open a couple of weeks ago - we assumed it just needed new batteries so when I was asked last night at about half ten if I'd got the safe working because she absolutely, positively needed stuff out of it for this morning.....
End result was this.

This POS cheap keypad was the culprit.

Turns out, if you're looking to buy a Yale Fire Safe, bear in mind that of the two key functions of a safe:
1. Keep stuff safe.
2. Allow access to your stuff.
The Yale Fire safe will #1 ok, but will fail miserably on point #2. This keypad will definitely fail to work at some point in its life. Not in the first few weeks or months when you write your glowing 5 star review on Amazon, but it will fail and has been the same part they've used for 5 years+, knowing its a cheap, unreliable POS.
Yale helpfully have a master code they can give you, but that's useless if it includes any numbers from the faulty buttons. Their next solution? Call a locksmith and pay for it yourself loser.

