A police box is a public telephone kiosk or callbox for the use of members of the police, or for members of the public to contact the police. It was used in some countries, most widely in the United Kingdom throughout the 20th century from the early 1920s. Unlike an ordinary callbox, its telephone was located behind a hinged door so it could be used from the outside by anyone, and the interior of the box was, in effect, a miniature police station for use by police officers to read and fill in reports, take meal breaks and temporarily hold detainees until the arrival of transport.
The typical British police box contained a telephone linked directly to the local police station, allowing patrolling officers to keep in contact with the station, reporting anything unusual or requesting help if necessary. A light on top of the box would flash to alert an officer that they were requested to contact the station. Police boxes were usually blue, with the most notable exception being Glasgow, where they were red until the late 1960s. In addition to a telephone, they contained equipment such as an incident book, a fire extinguisher and a first aid kit. Labelled a "British icon" by the Plymouth Herald, the blue Metropolitan Police boxes, designed by Gilbert Mackenzie Trench in 1929, became Britain's most recognisable police boxes. The blue police box is associated with the science fiction television programme Doctor Who, in which The Doctor's time machine, a TARDIS, is disguised as a British police box.