One goal may be to keep out neighbors pets and other varmints. Most of the doors that offer some sort of electronic locking will do fine at keeping out unwanted pets. These use some type of collar key that unlocks the door for your pets. Most systems have only a single key type, so if you have neighbors using same pet door system, their pets could use your door. It may be worth it to get a system that has selective keys, such as the Staywell Infrared door.

Raccoons pose another problem altogether. They are very determined, rather smart, and strong. The only pet door we've seen that can keep the varmints at bay is the Power Pet door, that uses a hard lexan door and electrically opens and closes the door (the pet does not push the door open). This is a great door, but not cheap.