Smartwatches are great for this.

In fact, a smartwatch might be the ideal "second personal portable computer that's just for auth and banking" that is being proposed by various commentors here.

Requiring that everyone carry a smartwatch (or other smartwatch-based compute nugget) around to participate in civic life is a bit less onerous than requiring everyone carry around a smartphone; smartwatches are both cheaper and smaller.

And, to me at least, smartwatches are much more of an appliance than a smartphone is. Nobody's really begging to sideload apps onto their smartwatch, or to install an alternate launcher onto them, etc. Smartwatches just kind of "do what they should obviously do given the hardware design and HCI affordances" — kind of like a calculator.

As a bonus, unlike smartphones, most smartwatches to this day still aren't independently connected to cellular networks; so the average wiretapped smartwatch can't be used to surveil your location and activities in quite the same way that a wiretapped smartphone can.

Yeah, in low-fraud scenarios it's a very good idea. Otherwise, though, you have the problem of what happens when a robber takes it.

I'm thinking a ring type device might be better--put a pulse oximeter into it, you unlock it with your phone, it remains unlocked only so long as it gets basically perfect data from the oximeter, locks if it fails for a second. Thus said robber can neither snatch your ring nor cut off your finger and use it. I like the metal mesh straps that can hold my device very snugly against my skin without being tight and that would be good enough, but a looser strap would not.