Smart card, shoplifting and Wal Mart

If you  leave Wal Mart, your smart card says, good bye, nice shopping.  It can talk to the exit door. The shop lifting problem goes to small almost immediately.  All bags of goods in which the owner sends a good bye, likely honestly purchased.  Especially since expensive goods likely have the price beacon still attached.  So you open up Wal Mart to a host of python apps that go through the wireless messages, then hit the red/green buzzer the security guard carries, in his smart card..  Reducing shoplifting at Wal Mart would cover the entire cost of deployment.