Masquerade Gear Solid
An extremely simple, lightweight addon that adds the pants-messing feeling of everything going wrong in MGS.
Does what it says on the tin, and nothing else. Whenever something in Suramar city threatens to dispel your masquerade, the "spotted!" alert sound from MGS plays.
This addon still works with 7.1; WoW will flag it as out of date, but if you load out of date addons, it still works fine. And it should work fine indefinitely. As small as it is, it relies on very little of WoW's API, so the chances of it breaking are low. (I could give it a TOC update...but I can't be bothered.)
Things worth noting:
This addon works by scanning for NPC /say messages and then checking if the message matches a list of things which illusion dispellers are known to say when they catch a whiff of your fakery. This means the following:
-If someone else nearby triggers an NPC's dispel illusions, the sound will play even if you have nothing to worry about.
-If the NPC says something not on the list of known /say messages, the sound will not play.
-The sound will not play at all outside of the enUS localization.
-There are some demons deeper in the city that don't say anything, so when they spot you, the sound will not play. They're also much, much quicker to reveal you; no alert sound can save you from them anyway.
This method was chosen over scanning the combat log for "NPC starts casting Dispel Illusions" because the range on doing so is much larger, and thus the rate of false positives would also be much higher.
If you want to fix this by adding missing messages (if any), or by adding messages in other localizations, feel free. There's a reason this addon is distributed under the WTFPL license. Several reasons, actually.