I found some apps that operate as a spirit level (free, of course, because I’m cheap). Some are better than others. I thought it was a brilliant idea because, well, you just never know when you might need to level or plumb something on the fly. It could happen; I don’t use the flashlight app all that often either, but I’m hanging on to it. So I picked a level app that suited me, but upon playing with it I was confronted with the fact that even though the app works great on its own terms, the buttons on the sides of the phone prevent the phone itself from ever sitting level, so in practical terms the app’s useless.
On my phone, a raised area around the camera lens prevents the phone from sitting flat on its back, but Bubble Level (also free) appears to allow for that. That said, I’ve had Bubble Level for almost 4 years, and haven’t used it once. I guess it could still happen.
It shouldn’t matter whether your phone sits level, as long as however it sits is repeatable. The app should ask you to put your phone on a surface oriented in one direction, then the other. That’s a self-calibration that every electronic level I’ve used (and that’s a few) does.
This one asks me nothing. It’s strictly passive just like a real spirit level, simply responding to conditions; it’s very pared-down basic. There’s a horizontal and a plumb level, and a bullseye level too. That one seems pretty on despite the slight camera protuberance on the phone’s back, but maybe my desk’s planar level is a hair off-kilter.
Makes sense, but as I thought I made clear, this one strictly emulates your classic, physical spirit level: IOW, no degrees or anything else fancy. Like a real, basic, garden-variety spirit level, it just has slidy “bubbles” and the boundaries one customarily refers to. That’s it. I chose this way because I like the familiar simplicity, but this time simplicity proved not the better option.