Yeah. Those are the major concerns among everyday people, as having an implant would put their life at risk. No matter if there are health or security issues, they need to be of utmost concern before making implants a practical method for making transactions in the mainstream world.

For now, we would be doing fine with current wallet methods, but I believe that as society and technology advances, we might be able to see implants in our body in the future, when it becomes mature enough towards mainstream use. In some way, manufacturers would devise new security mechanisms, to ensure the safety of using implants on everyday people.

As I've stated before, it might not be Bitcoin, but instead a digital currency issued by governments themselves with their own implants and a full-fledged blockchain system. Just sharing my thoughts.