Cat Flap

 A cat flap, also called a pet door, is a small covered opening in a door, wall or window through which a cat can enter or leave. "Cat flap" is chiefly British usage; "pet door" is common in American English.

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In The Miller's Tale, written in the late 14th century, Geoffrey Chaucer described a low hole in a door "where the cat was wont in for to creep." In the story, a servant whose knocks go unanswered uses the opening to peer inside. The tale forms part of The Canterbury Tales.

Isaac Newton is often credited with inventing the cat flap, but the story is almost certainly a legend. It was circulating by 1802 and claimed that Newton cut one large hole for a mother cat and a smaller one for her kitten, overlooking the fact that both could use the larger opening. Cat holes had existed for centuries before Newton, and his biographers found no evidence that he kept a cat in his room at Cambridge.

The Oxford English Dictionary dates its earliest known example of the term "cat flap" to 1957, in the work of English novelist Angela Thirkell. Its earliest evidence for "cat door" dates from 1959.

One of the oldest documented surviving cat-access holes is in a door beneath the astronomical clock at Exeter Cathedral. During Bishop William Cotton's tenure, which began in 1598, the cathedral paid carpenters eight pence to cut the hole so his cat could catch mice and rats.

Cats had appeared on Exeter Cathedral's payroll long before Bishop Cotton arrived. Fourteenth- and fifteenth-century accounts record payments of 13 pence per quarter for "the cat," the sum was occasionally doubled, perhaps because two cats were employed.

Two original medieval doors in the cloisters of Chetham's Library in Manchester still contain openings through which the library cats once passed.

An electromagnetically controlled cat flap developed in Britain in the late 1980s used a magnetic element on the animal's collar to activate reed switches and release a solenoid-operated catch. Its US patent was granted in 1991.

Cambridge physicist Nick Hill developed a cat flap that reads an implanted identification chip after a neighbour's cat repeatedly entered his home and frightened his cat, Flipper. The first SureFlap microchip cat flaps, which use radio-frequency identification to admit registered animals, went on sale in 2008.

A 2025 Cats Protection survey found that 59% of cats in the United Kingdom went both indoors and outdoors. The report's 74% figure referred to cats that were microchipped, not to cats using cat flaps.

Sources: Oxford English Dictionary; Washington City Paper; English Cathedrals; Chetham’s Library; Google Patents; Cambridge Network; Cats Protection; Longman Dictionary of Contemporary English