This is a repost from the raidsecrets reddit. I was reading through the Vault of Glass related Grimoire cards a while ago when I had a revelation. The Grimoire card in question was "Mystery: Praedyth's Door". This was before I had played the Praedyth mission which puts a different spin on the meaning of the card than what I was thinking at the time, but I still think that my theory will stand without the card itself, the card was mostly just a stepping stone that helped me piece together other parts of my theory. I only recently realized that there's almost no way I can test this theory on my own because there are just too many possibilities, so I'm going to post it here hoping that the community will find it interesting and keep it in mind whenever they run the Vault. The Grimoire card "Mystery: Praedyth's Door" talks about how Praedyth is still trapped within the Vault and is trying to send out a distress signal but can only send out the signal whenever the "window" is open, whatever that means. Having not played the Praedyth mission yet, I thought this was a hint to get us on the right track towards the Vault's secret. The rest of the evidence I have comes from the launch version of Destiny before any expansions, so it would have been possible to figure this out from the beginning. I'm not sure where it's from, but in one of his interviews, Luke Smith said that he personally wrote all of the flavor text on the Vault of Glass gear. This pretty much confirmed to me that the flavor text was related to the Vault's secret. Praedyth's Revenge says, "Praedyth's fall isn't over… because it hasn't happened yet… and it will happen again." this would seem to be a pre-expansion indicator that Praedyth is still alive somewhere in the vault stuck inside of a time loop or something. The warlock's chest piece says, "Slept in the armor last night. Woke to feel my heart stuttering to the pattern of an unknown signal." This doesn't seem important until you realize that when looking down a sniper scope, like Praedyth's Revenge, you can hear your own heartbeat. It is incredibly faint and I've only heard it while looking down the scope in very quiet places while playing the game with headphones, but it's definitely there. All of this leads me to believe that in a certain spot in the Vault, under certain conditions, and while wearing Vault armor, and looking down the scope on Praedyth's Revenge, you will be able to hear your heartbeat beating unevenly, probably in either morse code or binary, and that it will decode into a message from Praedyth relating to the Vault's secret. The only problem is that I don't know where in the vault we would have to do it or what circumstances would put us into the spot in Praedyth's time loop where he is transmitting. TL;DR: Read the first sentence of the last paragraph. So, thoughts?