Digital Chains.
More than likely this will also be used to enslave all of their employees in much, much worse ways. Such as the app will know through a combination of GPS and accelerometer readings to know when and where you are working. The chronometer itself will know if you are on the clock or off the clock. Either way means Wal-Mart owns you in ways you will never be able to abandon or misuse to your benefit(s). You will most definitely be blacklisted should you be fired or quit for your refusal to work while off the clock as well.
If I worked for Wal-Mart, my “free” phone would never leave the building. It would live in my locker when I was not working. I would also charge it on company time.