If you have an active canine companion who constantly wants to be let outside and then back inside, you might consider installing a dog door. A dog door conveniently lets your dog come in and go out at will when you want to allow it; you can also secure the door when you want him to stay on one side of it or the other. There are some factors to consider before you purchase a dog door.
Decide what type of pet door you want. A patio door pet panel is the easiest to install: The panel simply slides into the upper and lower tracks of your existing sliding glass door. Door-mount dog doors, which you can install in wooden, metal, French or glass doors, require you to cut a hole in the door. Wall-mount dog doors require that you cut a hole in an exterior wall, creating a little tunnel through the wall.
Measure the widest part of your dog with a tape measure. The widest part of a dog's body is typically the shoulders or the hips, depending on the breed. Buy a dog door that's at least 2 inches wider than your dog's width.
Measure the standing height of your dog with the tape measure. Measure the distance from the floor to the top of his shoulders just behind his front legs. Because your dog will duck his head down as he pushes the dog door open, the pet door you purchase should ideally reach just above his shoulder.
Make a doggy door template. Draw your dog's width and height measurements out on a piece of cardboard. Cut out the template, and hold it up to your dog to determine whether the size is correct. If the door seems too big or too small, measure your dog again and make a new template. You need to have an accurate size before you go to buy a doggie door.
Determine whether you'd prefer a manual or an electronic dog door. Manual dog doors have single or double flaps that allow your dog to simply push his way inside and outside. An electronic dog door is activated by an electronic chip on your dog's collar that signals the door to open when your dog gets close.
Consider how much you want to spend on a dog door. Pet doors come in a wide range of prices. The least-expensive dog doors typically feature simple plastic frames and acrylic flaps, and cost less than $20 as of 2012. The most expensive dog doors feature infrared technology, self-locking mechanisms and personalized electronic "keys" to open the door. Although these high-tech doors offer a higher level of security, they can also run you over $1,000.