I don't have an S10+, and actually have never used Smart Lock - for me the (rear) fingerprint scanner on my Pixel 2 is better because touching that wakes the phone and removes the lockscreen, while Smart Lock only unlocks and I still have to swipe past the lockscreen, which is therefore less convenient than just using the FP scanner.

But as an experiment I just tried it with my Pixel and a few devices, and found that Smart Lock worked with a Fitbit device, a Logitech bluetooth mouse and an iPad. It didn't work with a Jabra desktop speaker (one of my most-used pieces of kit in the last year!). Neither my laptop nor my Samsung tablet would maintain a bluetooth connection when I wasn't actively transferring files, so were no use for this purpose. And I didn't test it with my kitchen radio because my wife is running a Zoom meeting in there and I didn't want to risk some audio app deciding the start playing when I connected .

 

I would have thought so. As long as it maintains a bluetooth connection that should work. But I've not tested (ironically I left my fitbit charging this afternoon, but didn't see this question until after I'd removed it from charge and put it back on).

Of course the things will run for more than a week without charging, probably longer if they just sit on a desk than if you are moving around.