Son in his room with another boy locks the door and takes while to open?

hello my son is only 15 and i am very concerned he may be doing drugs in his room, whenever his friend comes over he locks his door and if i knock it takes several minutes for them to answer and he looks ":roughed up" kinda.. I also hear some strange noises then one telling the other to be quiet like they are trying to be sneaky. Do you think i should put a hidden camera in there or am i over reacting?