The dog is part of the family. It is the official greeter to all visitors, hangs out with everybody, encourages you to take a walk regularly and provides intangibles too numerous to list. You and the dog are firmly bonded.

But there comes a time, usually about 3 a.m., when dear Fido becomes a real pain because he has to go outside. Being awakened occasionally is to be expected. But when an early-morning pattern starts to emerge, you have two choices: learn to wake up and go back to sleep quickly, or install a dog door.

There is also a daytime convenience consideration. It’s easier for the dog to let itself in and out than it is for you to schedule your day around required outings. And if there’s a new puppy in the family, the quick exit potential of a pet door may reduce accidents and speed up house training.

Most commercial pet doors are based on an opening in a door or wall with a flap that is fastened at the top. The most popular style of door has plastic flaps with magnets on the bottom, says Jason Perkins, presentation manager at Pet Smart. The flaps make entrance and exit easy for all sizes of animals, while the magnets keep the flap closed until the dog (or cat) needs to push it open.

One option for people with sliding glass doors is a clear panel with a dog door already in it. The panels fit a standard sliding door frame and are one of the easiest doors to install. The top is spring-loaded, so all the pet owner has to do is place the panel in the door opening. The panels tend to be the most expensive option, costing about $200.

If it seems like a dog door might be a good idea, read on for some things to consider.

What kind of door for which kind of pet?

Start with the location of the proposed door. The door should not exit to a street or driveway. The best location, Perkins says, would be into a fenced yard, where the dog is confined whenever it goes out.

Another consideration is the full-grown size of the pet. That cuddly puppy stage doesn’t last long, and the full-grown dog may not fit through a smaller door. The pet door should be sized so the top of the opening is about 1 to 1.5 inches higher than the top of the dog’s shoulders, according to Moore Pet Supplies, a pet door manufacturer. This ensures the dog’s back won’t hit as it goes through. The bottom should be low enough so the pet won’t have to step too high. This spacing can be especially important with breeds that may develop arthritis or hip dysplasia, advises Moore Pet Supplies.

For the winter months, Perkins said, you may want a door with a sliding panel that blocks off the cold when needed. The sliding panel can also lock the pet door.

Pet doors are usually sold in the form of install-it-yourself kits, he said, ranging in price from $19.95 to about $200. Most kits can be installed by a homeowner with basic tools and reasonable carpentry skills, he said, and come with directions and patterns for cutting the door hole.

How to install?

Once you’ve decided on the size and location, the choices narrow down to installing the door in the wall or the door. Each has advantages and problems. Part of the decision rests on who does the installation. Whether you install the pet door yourself or hire a professional, Perkins said, depends on your carpentry skills.

“Some people are intimidated about installing a door in a wall because there might be electrical wiring that need to be changed,” Perkins said. “And in some walls, the entrance might have to be framed in.”

Look before cutting into any door. If the door is made of steel or fiberglass, it may be a good idea to hire a carpenter. He or she will have the heavy-duty saw and specialty blade required to cut through these dense materials.

What about keeping critters out?

While the basic pet door concept remains unchanged, the high-tech world hasn’t passed over the lowly dog door, Perkins said. Some of the former concerns or liabilities of dog doors have been addressed.

For example, there is the fear that stray animals might find their way into the house through the dog door. In particular, raccoons and skunks could wreak havoc on your home’s interior if they got in.

“I’ve heard of stray cats getting in a house through an open pet door,” Perkins said. “But I don’t know of any raccoons or skunks getting in. Besides, there are new doors that eliminate that potential.”

Radio-controlled locks, with the key attached to the pet’s collar, can eliminate unwanted visitors, Perkins said. The radio collar door can have different keys for multiple dogs so there is no danger of unwanted entrance.

If your pet won’t use its new door, open the flap and tape it open. After a few days, lower the flap halfway. Gradually, the pet will figure out that pushing the flap opens it.

Eventually, the pet door may eliminate early-morning comfort calls. It will allow you to slumber in peace, secure in the knowledge that a mess won’t greet you first thing in the morning.