Portal Emancipation Grid
This tutorial shows how to make the emancipation grids in Portal that prevent you from taking things into the elevator.
1. First off, make an area for the grid to go. It needs to be a gap of atleast 128 units wide and 128 units high.
2. Place two prop_static's, one on each side of the gap. Make their world models - models/props/portal_cleanser_1.mdl and rotate so they are opposite each other.
3. Make a brush 1 unit thick, as high as the models. Place it in the middle of each model and tie it to a trigger_portal_cleanser.
4. In the properties of the trigger_portal_cleanser, give it the name "cleanser". In the flags, check "Clients" and "Everything".
5. Make an info_particle_system. Place it 64 units above the ground and right in the middle of the trigger_portal_cleanser. In the properties, set the "Particle System Name" to portal_cleanser and make sure "Start Active" is set to yes.
*Note - Make sure it's angle is facing one of the prop_dynamics.
That should be it. Just add some lighting, an info_player_start and a prop_physics with the model set to models/props/metal_box.mdl, then go test it out.