I have a CAT s61, it comes with it's own camera app. I used to be able to do it with the camera app on previous phones that I broke, which is why I got a rugged phone. (also the IR camera and laser pointer.) I would just install one, but at a glance, all of the QR code apps seem like scams, and I haven't cared enough to do any research.

good-old `ZXing` ( https://github.com/zxing/zxing ) does the job for me nicely, supports non-QR codes, and contains practically zero BS. The only downside IMO is the forcefully-narrowed scan window, which can cause complications with extremely large QR codes, as the pixels get a little blurry and decoding gets harder for the software.

Edit: you can find it on Fdroid or probably on the project site/page. It's not getting updates, but why would my QR scanner need those, anyways..... also Google doesn't want it to be published anymore, iirc due to it using relatively ancient APIs.

Although the recognition is hit-and-miss. A dedicated QR reader will grab the QR nearly instantly as soon as it is visible to the camera.