ClickDetector is used to make an object able to be selected, and if applied, perform an action. To apply it, select a brick, then go to Insert > Object > ClickDetector. If you apply a script to purchase a object by clicking, then when you hover over the object, your cursor will turn to a hand, and if you click, the script will be executed. You can also use this technique on doors, eg. placing a ClickDetector brick that when selected sets an object CanCollide setting to false, allowing passage. Good for making doors and such. At an unknown date, the ClickDetector pointer was revamped.