Objects in the window

I want some of my events to only work when the objects are visible on the screen, and not work when they're not. Its a platformer game, and I dont want an enemy that spawns in the other end of the level to move before it is in the screen window (means when my player is around the enemy).

I tried "Object is in the Play Area" and "Object is outside the Play Area", but I guess the whole frame counts as the play area, cause the enemy is still moving. The way I used to do this was to have a huge, invisible box blocking the whole screen and simply add "Enemy is overlapping BigBox" to the movement enemies, but I got told that this is big, unecessary use of CPU. I dont remember what I got suggested, but what do you guys do in this case? Oh, and another thing. Will the events that move the enemies use just as much CPU even tho they are not moving the enemy as in when they ARE moving the enemy?

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This can be used to activate objects once they get close enough to the visible part of the frame, and deactivate them when they are off-screen. They currently deactivate when 32 pixels off-screen (32 was chosen because of the objects size).

Yea, this seems to work :) Thank you very much :)