How to make an automatic door?

I am trying to build an automatic door. I am more of a builder. I have already created the doors design and now I just need the functions for it. I have the invisible brick with can collied turned off so you can walk over it, and I also have the onTouch object in the invisible brick. How would I connect the invisible brick to change the size of a certain brick though? Also I do not want to use free models.