Abstract: A cart immobilizing mechanism responding to signals prescribing a permitted use area for the cart is contained entirely within a wheel of the cart. This mechanism preferably includes a circuit board containing a radio frequency receiver, a decoder, and a logic driver. The mechanism also includes a solenoid device. When the receiver detects that the cart has been moved outside the prescribed use area, the solenoid device is energized to drive its armature into an opening in a non-rotating shaft supporting a wheel, thereby locking the wheel against rotation and immobilizing the cart.