apparatus for deterring unauthorized use and removal of steel or steel - and - plastic constructed swivel - wheel shopping carts by preventing the free movement of one or more of the installed wheels after the cart is moved a predetermined distance . a braking device , fully contained within a wheel , measures the distance traveled beyond an activating point by counting the number of rotations made by the cart wheel and compares the count to a preprogrammed stored attribute that defines the allowable distance the cart is allowed to travel once outside the shopping facility . depending on the direction the cart is travelling , the counter is &# 34 ; armed &# 34 ; or &# 34 ; disarmed &# 34 ; when the cart passes over low - frequency magnetic arrays placed at the entry and / or exit of the shopping facility .