In the beginning, it was just about getting rid of the keys to his office.

American biohacker Amal Graafstra, 40, decided in 2005 that he wanted to be done with such archaic technology "from like 700 BC." He looked at iris scanning and fingerprint reading as solutions for opening his office door, but decided those options were expensive and unreliable.

Inspired by the way pets are commonly tagged, he settled on a safe radio-frequency identification (RFID) implant. "I used to say that if I was beaten up and naked in the back alley, I still want to get into my door," he told Mashable Australia.

More than decade later, Graafstra now travels the world talking about the underground world of biohacking — people merging their bodies with technology. In 2013, he founded a site that sells home implant kits, Dangerous Things, and in one particularly popular stunt, he modified a gun prototype so it could only be activated by one of his implants.

Amal Graafstra. Image: Amal Graafstra/supplied

Visiting Sydney, Australia for an event on transhumanism sponsored by the video game Deus Ex: Mankind Divided, Graafstra arrived in the country with four sub-dermal implants. They include a near field communication-compliant (NFC) tag and a UKI chip on which various payment or transit applications can be loaded. Just picture your train card, but in your thumb.

Most implants can be installed with a needle, a process said to be about as painful as a bee sting.

According to Graafstra, there's been a steady rise in implant interest, but what he called the "killer app" is yet to emerge. That means implant technology with a use so helpful and ubiquitous that it will finally convince the public at large to have a small chip inserted under their skin.

"Aesthetic modification ... speaks to an idea that you weren't perfect to begin with."

"It's not going to be getting in your house, because there are so many locks and keys," he said. "The 'killer app' for me is payment and transit. If you can get rid of the keys and wallet with one device, then I think that's it."

Body modification is an ancient custom, but one that's often been socially fraught. Plastic surgery is increasingly acceptable, but most people would probably still prefer friends and colleagues not know about their face lift.

In Graafstra's view, implants sit apart from cosmetic modification. Rather, it's about augmenting your body — giving it capabilities it never had before and never could have biologically.

"Aesthetic modification ... speaks to an idea that you weren't perfect to begin with," he suggested. "That's different from the dissatisfaction of somebody saying 'I don't have the ability to talk to machines.'"

"That's our dissatisfaction," he laughed.

An implant before insertion. Image: Amal Graafstra

Attitudes are changing as people become more familiar with the idea of implants. "In the beginning it was people just saying 'you're crazy, or you're working for the government or the devil, or both,'" he said.

Now their objections are more mundane: "That's well and good for you, but it's not for me."

Through Dangerous Things, Graafstra has helped show that implants can be safely installed with the right precautions, and now he wants to push the boundaries further.

Graafstra wants to build a bridge between a person's biological identity and their digital identity by hacking the body.

"The idea is, you could go to a bank and open an account and load a banking app onto your implant," he explained. "Now that implant can do banking and transit, and maybe even secure your data, like your emails or communications."

He's also hoping to showcase the safety capabilities of implants. His modified gun made international headlines, but Graafstra's point was that a gun is a deadly weapon and should only be used by the intended operator — something implant activation could definitively ensure.

"If you have kids in your house, or a situation where someone breaks in, you don't want the wrong person operating it," he said. "Other smart guns that use fingerprint reading or use wrist bands or rings present a reliability problem. With an implant, you're never not going to have it."

Thanks to Hollywood and films such as the The Manchurian Candidate, one of the main concerns people raise when faced with an implant is tracking and privacy.

Graafstra emphasised that his implants aren't tracking him, they are logging, much like when you use a tap-and-go bankcard. Your credit card or train card isn't tracking you exactly — it only "wakes up" and hands over your data when held near a terminal that can read it.

There are of course privacy issues when using your implant outside the home with third parties, such as a café's payment station. In other words, he argued, an implant will not log you more than the credit cards and transit cards you use daily. It's just more convenient.

While there is still a stigma attached to implants and modifying the body, Graafstra believed the movement is starting to capture the attention of people of all ages. "The oldest person I've ever put an implant into was about 72-years-old," he said. "And I've personally done over 1,200."

Still, people are more likely to be comfortable with an implanted medical device, despite their insertion typically being more invasive.

"How a pacemaker works, or a deep brain stimulator, those kinds of devices are terrifying to me," Graafstra said. "That's a real serious integration with your biology."