A lot of Androids (the ones I have kicking around) don't have a scanning app that comes with the OS so you have to install one, I think most of those use a commercial or open source QR code scanning library that they got from somewhere but not always the same somewhere.
For my three-sided cards I finally realized I can just put a URL to a web-based QR code scanner on the back of my cards and not have any trouble navigating all the scammy looking listings you see when you look for a QR code reader on the play store.
