Create customized QR-code scanner

I'm looking for someone to help create a customized QR-code scanner/reader for on-site attendance system. Employee will scan a QR-code to sign in and sign out they're attendance at the site, very similar to fingerprint attendance system. The catches are: 1. There should be no history available, so employee will have to actually, physically scan the codes instead of using the history list to sign in and sign out. 2. The codes should only be readable/scan-able using this custom software and no other scanner/reader readily available at the market. 3. For now the system is intended for android-based phones only, but later it might be expanded to include all other smart phones OS out there. I'll leave it to your imagination on how to achieve said objectives. Please note that we don't have a big budget for this project, so I may end up not hiring anyone at all if you ask too much. Thanks and happy bidding. :)