According to the Scriptures, the "mark of the beast" is received on the right hand or forehead. With modern technology, it is very possible that this mark may be directly linked with a computer chip. But regardless if it is or isn't, everyone who is living immediately before the return of Christ will be forced to take this mark in order to buy or sell anything:
"He also forced everyone, small and great, rich and poor, free and slave, to receive a mark on his right hand or on his forehead so that no one could buy or sell unless he had the mark, which is the name of the beast or the number of his name. This calls for wisdom. If anyone has insight, let him calculate the number of the beast, for it is man's number. His number is 666" (Rev. 13:16-18).
http://www.evangelicaloutreach.org/markbeas.htm
In the USA, 98-99% of all transactions are cashless, and cash represents about 1-4% of bank deposits. Smart cards and biochip pet implants are in wide use in Europe. Christians strongly suspect that this "mark of the beast" prophesy will be implemented by technology that exists today, the biochip implant (syringe implantable microchip/lithium transponder), or an invisible tatoo designed to go in the right hand or forehead.
666 watch
http://www.av1611.org/666/