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An electronic serial number (ESN) is a unique identification number embedded by manufacturers on a microchip in wireless phones. The ESN is automatically transmitted to a base station when a call is made. The carrier’s mobile switching office then detects the ESN and checks the validity of the call to prevent fraud.
The electronic serial numbers are used in devices using code division multiple access (CDMA) technology. A 32-bit ESN has 8 bits representing a manufacturer code, 18 bits for a unique serial number and 6 bits reserved for future applications. The numbers are also used for time attendance and registration tracking.