A system for monitoring and controlling shopping cart usage comprises a wheel assembly that attaches to a shopping cart. In some embodiments the wheel assembly includes a wheel, a brake that can be activated to inhibit rotation of the wheel, a controller that controls the brake, a VLF receiver, and an RF transceiver. The RF transceiver may, for example, operate in a 2.4 GHz frequency band. In some implementations, the RF transceiver may be used to detect entry of the shopping cart into a checkout area of the store, and the VLF receiver may be used to detect that the shopping cart is exiting the store. The controller may activate the brake if the shopping cart attempts to exit the store without first passing through a checkout area.