Dunno about other Androids, but just hitting the "power" (or wake or whatever it is) button 3 times on the Pixel pulls up the camera app. Even if the phone is currently locked. I think you can set it up so one of the physical buttons takes a photo as well but not 100% sure.

[–] twoface@sh.itjust.works 3 points 1 week ago

Yeah, the Sony phones do that as well. The special part of the camera button is that it acts like one on a proper camera. If you half press it (you can feel a slight change in resistance when you hit the spot) it engages the focus and then you can press it fully to take the picture.

I was able to program the Bixby button on my Samsung S10+ to take pictures as well, but it lacks the half press feature.