Privacy: Biometric Recognition
You're probably already familiar with biometric recognition. Maybe you use your front-facing camera's facial recognition to unlock your phone, or a fingerprint reader to unlock your computer. "Biometric" simply means biological verification. So any sort of system that relies on your biological features - such as facial recognition, fingerprint, eye scan, walk, and more - counts as a "biometric recognition" scan. And these are all systems that increasingly popular and only continuing to get cheaper and become more widely adopted.
How to Defeat Biometric Recognition
Due to so many business trying to safeguard their secrets, it's hard to say exactly which systems are most popular. Due to the prevalence of cameras and how recent gait recognition is, I'd venture to say that facial recognition remains the cheapest and therefore most popular form, and fortunately that one is easily defeated: aviator sunglasses and a hat. I can't cite a source here except to say "a credible law enforcement source who I trust." This friend claims that because the technology is so new and most facial recognition software isn't high end, most systems are easily fooled by a baseball cap and aviators. However, for more high end systems and the more cautious individual, there are things like reflective glasses frames, creative makeup choices, and hairstyles that cover part of your face.
Gait recognition can be easily defeated by putting a rock in your shoe, a technique used by Julian Assange when he fled to the Ecuadorian embassy back in 2012. I also read that it can be defeated by wearing loose-fitting clothing, though admittedly I was unable to find the source of this when writing this page. If the rock thing sounds painful, don't worry. I suspect gait recognition is not very widely adopted yet, but rather was created as more of a "proof of concept" thing. I doubt it would be used in a daily life context.
Fortunately at the time of this writing, I don't think technology has advanced enough to warrant concern about other types of biometric identification. In researching this page I found an article listing some proven but unusual types of biometric identification including your butt print and your ears, and recently another study proved that your sphincter is basically a fingerprint. At this time, I find these interesting and sometimes amusing, but I don't think they're enough to be concerned about. Right now I think facial recognition should be your primary concern. Fortunately, in the wake of COVID-19, the wearing of face masks has become sociall acceptable and I think we should use that our advantage. Face masks have already been accounted for and adapted to by facial recognition softare, but they still help and it's unlikely that every system out there has made this adoption or even that the users have upgraded accordingly.
It should go without saying that I don't recommend using a fingerprint or facial scan to unlock your phone. One woman unlocked her husband's phone by using his fingerprint while he slept and studies have repeatedly shown that phones can be unlocked with pictures. I recommend using a password or pin. Some companies claim the biometric data stays on your phone, meaning they won't sell it or use it to train their own facial recognition software, but we have no way of knowing if that's true and either way that could easily change someday with no warning.