Stealth Alerter detects if someone near you uses a stealth ability, and logs a message in your chat window. I originally wrote this AddOn in 2009, because a very annoying Rogue named Ýes used to hang out in Wintergrasp on the Shu'halo server where people were fishing. I've also found it useful in raids, battlegrounds and arenas.
The following actions are detected: Camouflage (Hunter), Draenic Invisibility Potion, Greater Invisibility (Mage), Invisibility (Mage), Invisibility Potion, Lesser Invisibility Potion, Potion of Minor Invisibility, Potion of Trivial Invisibility, Prowl (Druid), Shadowmeld (Night Elf), Shroud of Concealment (Rogue), Stealth (Rogue), Stealthman 54, and Vanish (Rogue).
"/sal on" enables Stealth Alerter and "/sal off" disables it. "/sal" while enabled lists all options and settings.