As a bonus, the random code's continuous signal provides precise information about the time.

ECONOMIST: Global positioning: Accuracy is addictive | The

By changing the frequency of a radio transmission many times a second, causing it to leap around in an apparently random fashion, a radio signal could be made almost impossible to intercept.

ECONOMIST: Player-piano pioneer

Only a receiver programmed with the same random sequence would be able to follow the signal as it hopped from one frequency to another.

ECONOMIST: Player-piano pioneer