Cat flaps are the greatest. Cats can go outside for sunshine and fresh catnip. They can come inside for kibble, water, and climate-controlled comfort.

You'll like it because you won't have to let the cats in and out, and you won't have to clean the litter box as often. When it was just Milo and me, we didn't even have a litter box. When Melissa and I moved in together her cats were used to one, so we keep it around, but they hardly use it, especially in warm weather.

When Melissa and I go out of town for the weekend, we take the dog to her mom's, but we don't have to worry about the cats. With continuous feeders and a cat flap they're fine for two or three days.

A few years ago my brother Eric put the first cat flap in the door going from the utility room to the outside. As I later discovered, that meant having to leave the door open between the kitchen (which is nice and new and clean and peaceful) and the utility room (which is old and shabby and messy and noisy). The new cat flap goes in the door between those two rooms, and makes the house quieter and cleaner. It probably reduces our energy bills, because the utility room isn't heated.

Total project time: about an hour with setup and cleanup
Cost: $20 for the cat flap
Tools:

• Saber saw (nee Skil saw)
• Sawhorses
• Hammer and screwdriver to take door off hinges
• Electric drill (optional)

Instructions

Wedge a screwdriver under the door hinge pins and tap them out with a hammer. Set the door on sawhorses in an area where sawdust won't be a problem.

The Ideal brand cat flap I used includes a tracing template. There are two small tricks to choosing where to lay that template on the door. Both relate to the fact that a hole in a door can weaken it.

Trick Number One: trace the cat flap on the door's panels (the thin parts), not on the door's frame (the thick parts). Trick Number Two: trace the bottom of the flap 5 to 6 inches from the bottom of the door so you won't compromise the bottom of the door frame. That's the distance Ideal recommends, and it turns out to be the right height for the cats. Notice how in the pictures they're looking right through the flap.

If you aren't experienced with a saber saw, there's one other trick you may need to know. How do you get the saw started in the interior of a door? I used a cordless drill and a large bit to drill a starting hole a little bigger than a pencil. You can also plunge saw. Rest the saw at an angle to the wood, with the front of the saw's metal platform touching the wood. Then press the trigger and gradually tilt the saw blade into the wood.

Movie: Milo's First Trip Through the New Cat Flap

AVI Format Movie (1.5 Mbytes)
QuickTime Format Movie (1.8 Mbytes)

If you watch the movie, you'll see Melissa's hands holding Milo up to the flap. You'll also hear me mumbling "action." Also, this was actually the third or fourth attempt at capturing this special moment on film. When I was in biology, this is what we called nature fakery. It really makes you respect the guys on the Discovery channel. I'll bet the orangutans show up to work stoned, and the rhinos are all catty prima donnas who sleep with each other's boyfriends.

Fine Points of Having a Cat Door

The Ideal cat flaps have a lock, so you can leave the flap totally open, totally locked, or set it so the cats can go in but not out, or out but not in. Why? Well, for instance, if the cats have a vet appointment the next morning you might want them to be able to come in, but not go back out so you'll be able to find them in the morning.

The lock is slightly problematic. The cats sometimes trip it and lock themselves out. I generally wedge something into the lock to keep it in the open position.

I've seen opossums, raccoons, skunks and ground hogs in my yard. When I first put in a cat flap I was worried about other animals coming into the house. After four years we finally had another animal come inside. It was a grey cat. The other cats are apparently friends with it, judging from the fact they don't raise a fuss (though the dog does).

To avoid unlawful animal entry, PetSafe makes a line of electronic pet doors. They won't open unless they sense a signal from a special collar your pet wears. It strikes me as too expensive and too complicated to rely on, but it's another option.