Remote Screen Secrets Triggering
Remote Screen Secrets Triggering is the process of triggering the Secrets on one screen from another. There are several ways of doing this.
2.10 and older
In older builds of Zelda Classic, the only way to accomplish this was through clever use of Boss Flags. The engine keeps track of one Boss Flag per Level. The Boss Flag is a boolean that starts as 0, but is set to 1 when: (1) Link kills all the enemies on a screen (2) while on a DMap with a Level greater than one and (3) the Dungeon Boss Enemy Flag is checked for that screen. Once the Boss Flag for a given level is set, all enemies in rooms with the Dungeon Boss Enemy Flag will be dead when Link enters the room. Therefore, Secrets in those rooms will be triggered by the Enemies -> Secret screen flag. By using a hidden Fire enemy, or, in more recent builds, a Trigger enemy, you could trigger secrets remotely.
Newer builds greatly simplify this process. In Screen Data, tab 3, there is a tab titled Room State Carryover. If you want secrets on one screen to trigger secrets on another, all you have to do is put the Map and Screen coordinates of the Screen whose secrets you want to trigger remotely into the Room State Carryover.
It is also possible to trigger Secrets remotely using Scripting. The methods of accomplishing this are too numerous to list, and limited only by the designer's imagination.
As while the trigger enemy (which is a none type enemy) can still be used for remote screen secrets triggering in 2.50 and up, it is merely left in for compatibility with 2.10 and shouldn't be used in modern quests.