In my spare time I like to make stuff. One of my best devices is my automatic door opener. It opens your door when you put the access card over the switch. Your door still can be pushed open or closed, so this won't cause any problems.
(clip-art used was from free clip-art sites)
Step 1: Materials
-An old RC car (I used an old batman one)
-Alligator clips/Nine volt battery clip(useful to connect to nine volt battery, if that's what you're using.)
-Strong, thin magnets (neodymium work well)
-Old Credit Card
-Poster board (paper could be used, but isn't as strong)