The earliest pitchpipes were instruments rather like a recorder, but rather than finger holes, they had a plunger like a slide whistle's (also known as a swanee whistle). The pipe was generally made of wood with a square bore, and the plunger was leather-coated. On this plunger are marked the notes of either the chromatic scale or the diatonic scale, and by setting it to the correct position, the indicated note will be produced when the instrument is blown.
Pitchpipes of this sort were most often used in the 18th and 19th centuries in churches which had no organ to give the opening note of a hymn. They are now quite rare, and hardly ever used for what they were intended, but may still be used as an alternative to a tuning fork. They are also useful for establishing what pitch standard was being used at a particular place and time.
Another kind of pitchpipe is a tuned-reed instrument which can produce only a few notes. These are used for tuning instruments; for instance, one used for tuning guitars produces the notes E' A' D G B e. These are also used to "give the note" to a capella singers.