Detect Magic in the vault

[SelinarYaez]

From what I read gauntlight is protected by magic and to a lesser extent the keep. This means using detect magic anywhere will always detect magic, correct?

Re: Gauntlight is magically protected from damage, as
described on page 215. This protection has bled into
the surrounding ruins somewhat, slowing the usual
rate of decay over the past 500 years.

[James Jacobs]

It would, but more in the center at the actual Gauntlight. And you shouldn't use this as an excuse to make it harder to use detect magic for what it's intended for, but instead to give the players a potentially creepy or unsettling insight into the power of the dungeon they're exploring.