It is something holistic, I think. It is Antichrist's parallel to the mark on the forehead of the faithful ones, in
Revelation 14:1, right after Rev. 13:16-18. In Rev. 14:1 we read that the 144 000 sealed Jews had the name of the Lamb and its Father's name written on their forehead. Thus the followers of Antichrist (the Beast) have Antichrist's name on their forehead, or the number of the name of Antichrist, 666. I do not think this is a single, physical thing, it's something holistic, something primarily spiritual. It means that the followers of the Beast are sealed by Antichrist, have his stamp on them, something that marks them as belonging to Antichrist, as Antichrist's followers and worshippers. I do not think that John of Patmos primarily thought of a physical mark or a microchip, even if a voluntarily taken microchip
can be a result, a symptom of your allegiance to Antichrist, your being marked by him, as his follower. This is an important distinction.
Not being able to buy or sell without "the mark of the Beast", does not primarily mean that you cannot operate in society without "the mark of the Beast", in a physical sense, although this may be, in the end, the result of not having the mark of the Beast. What it means, is something deeply spiritual, again something holistic, it means that you are taken out by God from the "world", that you are chosen by God, to serve God and his creation, not Antichrist and Babylon, the evil civilization, and that this make you an outcast in this world, one of the meek who shall inherit the earth, one of those whose kingdom is not of this world (John 18:36). This can cause you to get into trouble with this world, but it does not mean that you physically cannot buy or sell in the end times, otherwise pretty much no one in the western world would be saved, only the wild indigenous people in the forests, and some poor farmers in the fringes of society in the third world who are able to not handle money. No, this is again something spiritual, primarily, but it can very well cause you to abstain from a smartphone (which is one of the technologies that can lead you to become full of Antichrist's spirit, i.e. become marked by the Beast, but it is not in itself the mark of the Beast, because this mark is primarily something spiritual).
But can you voluntarily want to be microchipped and not be marked by the Beast? I very much doubt it, although the "mark of the Beast" is not exactly the same as a physical microchip. First you are marked by the Beast in your spirit, and it eventually leads you to become marked by the Beast on the body and in all your works.
No technology is in itself the mark of the Beast, it is for example possible to be involuntarily microchipped by the 666-system (high-tech society), as has happened to pet animals and to one of my close friends who is a mental patient and also considered a criminal. They are microchipped in case they would escape. This is the reason why I don't think "the mark of the Beast" (which will make you an unbeliever, unsaved, if you take it, according to the book of Revelation) is just a physical microchip inserted into your right hand or a stamp or a tattoo on your forehead. Just the mention of the forehead eliminates this interpretative possibility. This is not to say that the microchip and the cashless society has nothing to do with "the mark of the Beast" and the 666-system. As you may notice, the whole issue is very complex. In any case, the kingdom of the Beast and the 666-system is
the climax of Babylon/Babel, a veritable
tower of Babel, where man wants to be God and reach heaven through high-tech, AI (Artificial Intelligence) and VR (Virtual Reality), polluting and destroying nature in the process. If you like this process, this direction of society, or not,
pretty much there goes the dividing line between those having the spirit of Antichrist and those having the spirit of Christ.
Having "the mark of the Beast", does not mean to be dependent on high-tech in your life. If it would mean that, all sick people who are dependent of medications and wheel chairs and other products of high-tech, would automatically be filled with the spirit of Antichrist. No, to have "the mark of the Beast" is something completely holistic, it is to be filled with the spirit of the Antichrist, the spirit of high-tech, the spirit of
transhumanism (see also
this Swedish blogpost about it), wanting to become God without God, wanting to replace God's holy creation with something artificial, with AI and high-tech, Antichrist's paradise.
Therefore, be careful to not play with fire if you have a smartphone or a laptop or use VR technology. Be careful that the spirit of Antichrist, the prideful, megalomaniacal spirit of the high-tech 666-Beast-system (in
Revelation 18 it's very clear that the Kingdom of Antichrist, Babylon, is the so called "civilization", or the climax of civilization, high-tech society) does not fill you more and more. Then you enter a kingdom which will soon fall, and you with it. Then, if that happens, you might miss
the Rapture, and maybe then only the bowls with the wrath of God, the end time disasters which will collapse Babylon (which the bowls of
Revelation 16 are symbols of*), can save your spirit, so it becomes meek again, meek like the spirit of the dogs, foxes or chicken. There is salvation in poverty and humiliation.
But we are very, very close to the day
when the image of the Beast becomes alive, described in
Revelation 13:14-15, which I think has something to do with what technology pope
Ray Kurzweil calls "the singularity", when high-tech, AI and VR really takes off, exponentially.
Kurzweil now thinks this will happen sometimes during this decade:
"Earlier this week, at the SXSW Conference in Austin, Texas, Kurzweil made yet another prediction: the technological singularity will happen sometime in the next 12 years.
"By 2029, computers will have human-level intelligence," Kurzweil said in an interview with SXSW." (from this article from March 15, 2017)
Observe that before that he predicted the singularity to happen in 2045 - he has revised this prediction (see this article on March 20, 2017).
"The Technological Singularity" is Antichrist's parallel and counterpart to the Rapture of the Bride of Christ, and it is Antichrist's and his follower's attempt to live like gods, without God (it is also one of the greatest signs that we are living in the End Times, and that Babylon's fall and the Second Coming is very, very near). If you aim for that rapture, the "Singularity Rapture", you will be "left behind", after the rapture of the Bride of Christ, and you will experience the full wrath of Mother Nature and God upon civilization and its pride, i.e. "Nemesis Divina".
In fact, the rapture of the Church and the rapture of Antichrist, may happen at pretty much around the same time, maybe with an interval of a few years, the latter leading to the takeover of the world by Antichrist (American prophet Tom Horn predicts that Antichrist will be revealed to the world and take over in 2025, see this youtubevideo). I think "the Singularity Rapture" is the same as what is meant in Revelation 12:7-12, where Satan is cast down from heaven to earth, he will reveal himself to the world left behind after the rapture of the Church, he, the prince of this world, and his angels, will come to their own people, he and the "aliens"/"extraterrestials", and will finally reveal themselves and their dark technological and spiritual secrets. And Satan and his angels are not some red fauns with pitchforks in a medieval hell of torture and pain, but like kings and lords and rich people in this world, "civilized", but in the negative meaning of this word (if you have heard how the anarcho-primitivists use the word, what a valor it has in their mouth), full of pride and willing to play God with high-tech, even performing spiritual and physical miracles. Don't be rich when this time comes to pass, so that you do not find your mate and your likeness in Satan and Antichrist and his angels, being then easily fooled by them and their high-tech miracles and counterfeit spirituality.
* the disasters in the book of Revelation are not literal prophecies, but archetypes of the disasters that will befall civilization in the End Times. In this way Global Warming and Peak Oil are prophecied about in this book, albeit not literally. Isn't it strange that a book in Antiquity predicts the collapse of civilization, which many secular scientists, people like atheist professor Guy McPherson, now predict?