While you could just cut a hole somewhere for your pet, for most owners, this is usually unacceptable for many reasons, if not looks alone. Like most purchases, the more you pay the more features you get. Some of the considerations and features that will affect price include:

* Size of the opening - Larger doors usually cost a bit more

* Door seal - A good door seal greatly reduces heating and cooling losses if the seal is good. It also helps to keep out bugs.

* Reliability - The cheapest designs rarely last long. Look for doors with hard plastic doors for a much longer life. The soft vinyl "flap" type doors may tear over time, and can be hard to clean. They also tend to deform causing a poor weather seal. We've had raccoons cut right through locked soft plastic doors to get in. So don't count on them to hold back the most determined varmints!

* Electric Door Locks - Doors with a locking system can prevent outside strays and varmints from entering your house. They all work by having your pet wear a collar with some type of key. When the key is close to the door, it unlocks. Some of the cheapest keyed solutions work poorly, so look at our reviews for more about which ones really work. Some of these even have different coded keys, so that two neighbors can use the same system with different keys.

* Direction control - Most pet doors above the cheapest level offer some kind of manual direction control beyond allowing your pet to go in or out when they want. These have settings to allow pets to go out, but not come back in; to come in, but not go back out; or completely locked from going out or in. Your pet door may include a board or shield that fits over the door to completely close off the door.

* Powered door - The most advanced pet doors will sense when the pet approaches the door and electrically open the door for the pet. These designs also have a locking pin in place when the door is closed. While expensive, these ensure raccoons and other uninvited guests can't get in. Other lower-cost doors are not all that effective at stopping raccoons, even those with electronic locks. Smaller pets seem to like these type doors, as it requires no effort and no door hits them on the back as they go through the door as with other push-through flap designs.