From Global Pet Expo, a very techie microchip cat door.

Pet-Mate had an amazing assortment of electronic Pet Doors at Global Pet Expo. They manufacture them for dogs and cats, but one of the most advanced is their Cat Mate Elite Microchip Cat Door. It uses R.F.I.D. technology to offer major advancements in pet access control. To enter the house, the animal must have a Microchip ID from a Veterinarian implanted in the cat’s neck, or a unique Cat Mate electronic Collar I.D. Disc (not included). Any animal can exit through the door, provided the 4 way electronic lock is not set to ‘In Only’ or ‘Locked’. The door can be programmed for up to 9 cats, which will keep strays and the neighbor’s cats out. The LCD display shows selected entry and exit lock status, cat location and time since the flap was last used - for up to 3 cats. Cat location is indicated via arrows, which show the last direction of cat, toward indoors or outdoors. The cat door also features a timer function. You could set it for say 11 PM to 7 AM which will keep cats in at night. Uses 4 AA batteries which should power the cat door for 6 to 9 months. (Batteries not included.) Cat Mate Elite Microchip Cat Door has a MSRP of $199.95. There are many other high tech cat and dog doors starting as low as $24 at the company website:

http://www.pet-mate.com/