You may create the trigger inside your script this way:
_trigger = createTrigger ["EmptyDetector", _position];
_trigger setTriggerActivation ["ANY", "PRESENT", false];
_trigger setTriggerArea [_maxrange, _maxrange, 0, false];
_trigger setTriggerType "NONE";
_trigger setTriggerStatements ["this", "", ""];
_trigger setTriggerTimeout [0, 0, 0, false ];
Then you may check
list _trigger
every desired time period, the list of the trigger will keep updated all the time until you delete the trigger.