Check if trigger is occupied

Instead of detecting WHEN a trigger is entered, I want to check at any given time whether a trigger is empty or it is occupied by a collider.

Is this possible with C#?

bool isOccupied;

void OnEnterTrigger(){

void OnExitTrigger(){

Was that really so hard?

If you have multiple things that could enter, replace the bool with a count.
If you want to know what the things are that have entered, replace the bool with a List