Simple yet effective can be made easily.
Step 1: Internals
The red dot sight holds a laser which let's it's beam out at the bottom and at the top you put the laser in the middle of the box. May sound hard but once you look into it it is already aligned.
Step 2: Trigger
This starts the red dot and the spring with the lego piece act as a trigger to hold down the laser pointers button.
Step 3: Laser On
This is the laser on and you can see it fits the laser in the box also the laser may seem too bright but the camera did that. Also the red dot sight is really not a red dot it's just a laser and you alight it while looking down the bare box.