New technology made many changes to the way the police did their work in the 20th century. Some discoveries, such as fingerprinting, 1901, and, right at the end of the century, DNA testing, were new ways of catching criminals. Most were ways of allowing police to move faster and communicate with each other more quickly. Police began to use bicycles in 1909, radios in 1910, cars in 1919 (although it was not until the 1930s that cars and motorbikes were used regularly). Closed circuit TV has changed police supervision of difficult areas as well as speeding and other traffic offences.

As Sir John Fielding realised back in the 1750s, (see Gallery Crime Prevention 1750-1900), information is crucial in identifying criminals. In the late 20th century, computers opened up enormous opportunities to hold and search far more data than could ever be done manually. The National Police Computer holds records on 25 million people and can be searched in all kinds of ways, including the criminal's way of operating. This has led to some concerns about how far ordinary citizens should be allowed to see what information the police hold about them.