how about this-

public double radius = 1;

private Transform myTrans;

Start()
{
    // This makes it so that you don't need to do as many inefficent
    // dynamic searches, assuming you want to do this every frame
    myTrans = transform;
}


// Then, wherever you need to do the check-

GameObject[] foundObjects = GameObject.FindGameObjectsWithTag("activated");

foreach(GameObject obj in foundObjects)
{
    ScriptWithBooleanOnIt objScript = obj.GetComponent<ScriptWithBooleanOnIt>();
    if(objScript == null)
    {
        // This makes sure that your object in question contains the script
        continue;
    }
    // This will also set the value to false if the object goes back out of range.
    objScript.booleanValue = Vector3.Distance(obj.transform.position, myTrans.position) < radius;
}

And then put a MonoBehaviour on every object you want to affect with this called 'ScriptWithBooleanOnIt' (name not important), and make sure it has a public bool called 'booleanValue'.