Here in lies a suggestion for DM's useing Mor-aths guild.
For the riddles, I have not entered any. I leave it to yer imagination to dream up the riddles for yer locked doors.
For when the wrong answer is imputed into the key pad. I myself set off magical traps such as Fire Balls and Lightning Bolts, but of course it is entirely up to ye if ye use traps.
Good DMin,
Mor-ath, God of Stealth and Silence