Detecting units effected by an aura?

I was wondering how to make a trigger that detects all units that come under the effect of an aura and to have a percent chance that the unit has a spell casted upon it.

I couldnt figure this out so i ended up just making a periodic timer and making the units picked all units around the unit with the aura and cast the spell on them. I dont really like this method. I also tried using the event units in range but it will not let me set a variable it only lets me select the unit that is already placed on the map.

So, every time a unit moves into the aura i want it to have have a chance of having a spell casted on it.

thanks

pick all units with the buff placed by your aura

im looking for a way to detect units effected by the aura IE if a unit comes under the effects.

and is the only way to do this by setting a periodic timer as event?

Yep. Either tha, or use the Abuff Aura module available in the resources section.

ues xecollider if the event is 'comes in range' (why use an aura here)

it does the timer thing already and the was-already-hit-since-it-came-in-range checks.