A church key initially referred to a simple hand-operated device for prying the cap (called a "crown cork") off a glass bottle; this kind of closure was invented in 1898. The shape and design of some of these openers did resemble a large simple key. Certain tin cans, notably sardine cans, meat containers, and tennis ball cans also used an attached "key" to open them. The first of these was patented in Canada in 1900.
In 1935, beer cans with flat tops were marketed, and a device to puncture the lids was needed. The same term, "church key", came to be used for this new invention: made from a single piece of pressed metal, with a pointed end used for piercing cans — devised by D.F. Sampson for the American Can Company, who depicted operating instructions on the cans themselves, and typically gave away free "quick and easy" openers with their newfangled beer cans.
There is sparse, and often contradictory, documentation as to the origin of the term "church key", although many people believe that the phrase is an ironic euphemism, as the opener was obviously designed to access beer, and not churches.
Another motive for assigning the device such a name could have been the fact that beer was first canned (for test marketing) in 1933 — the same year Franklin Delano Roosevelt signed the Cullen-Harrison Bill. This act, which predated Repeal of Prohibition, amended the Volstead Act, making 3.2 beer legal. Some experts have posited the term "church key" was a way to "stick it to" the religious organizations who had effected Prohibition in the first place.
All ordinary consumer beverages in cans are now sold in easy-open pull-tab containers, invented in the 1960s. But other cans containing liquid still require piercing, such as canned milk and some juice cans.
Many bottled beverages now come with caps that can be twisted off by hand, without requiring a tool to pry the cap off.