A cat flap (also known as a doggie door or pet door) is
a hinged flap set into a door, wall or window to allow
cats,
dogs, or other
domestic pets to
enter and exit a house on their own without needing a human to open the door.
They are very popular with cat owners, many of whom like to encourage their
cats' natural independence by letting them come and go at will — particularly in
the
United Kingdom where it is believed that about 90% of all cats (including
ferals)
have access to the outdoors, many of these via cat flaps ([1]).
Flaps for most dogs must be bigger and therefore are often constructed
differently; except in rural areas they tend to give access to fenced-in yards
or gardens rather than the neighborhood at large.
The simplest are just weighted flaps, but these can have problems with wind
blowing open the flap or making a rattling noise. A magnet on the flap addresses
this issue by holding the door in place when not in use, but not so securely as
to prevent access. Sometimes a flap will also have adjustable catches to
restrict the opening of the flap in one direction or the other — for example to
allow the animal to come in, but not go out again. More sophisticated flaps have
electromagnetic catches that can detect a matching
permanent magnet worn on the animal's collar and unlock the flap as the
animal approaches, thus preventing any other animals using the flap to enter the
house.
Devotees suggest a pet door should be set at a height so that the bottom of
the opening is just a little lower than the belly of the animal when standing.
Many animals prefer to use a flap with a
transparent flap, so that they can be sure there is nothing threatening
outside before leaving the safety of the home.
A wall-mounted flap with access tunnel.
The invention of the cat flap is often attributed to Sir
Isaac
Newton in the
seventeenth century; this story, however, is usually related ([2],
for example) without any sources to support it.
A cat flap in action.