The only biometric technology which does not measure the visual features of the human body. In voice recognition the sound vibrations of a person is measured and compared to an existing sample. The person to be identified is usually required to pronounce a designated password or phrase which facilitates the verification process. Voice recognition can be used on the phone, but has the weakness of technology is its susceptibility to interference by background noise.
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Claude Chappe built a fixed optical network between Paris and Lille. Covering a distance of about 240kms, it consisted of fifteen towers with semaphores.
Because this communication system was destined to practical military use, the transmitted messages were encoded. The messages were kept such secretly, even those who transmit them from tower to tower did not capture their meaning, they just transmitted codes they did not understand. Depending on weather conditions, messages could be sent at a speed of 2880 kms/hr at best.
Forerunners of Chappe's optical network are the
For more information on early communication networks see