the door slides vertically, pulled by a steel wire connected to a motor. The cable is attached (on teh door side) to the locking mechanism, so whenever it's down, it's locked.
unlocking and opening are pretty quick, although I never timed it.
With the old mechanism, it would be closed within...
This is not homework, although I am an EE student. If the solution is cool/complex enough, this might become a design project, although it'll most likely end up as something to do over the summer.
some time ago, I purchased a motorized doggie door. The dog wore a high frequency sound...