In some embodiments, the wheel units are placed on shopping carts and are used to determine whether {TAIL ~ particular shopping carts} are authorized to exit {HEAD ~ a store} 
In some embodiments , the wheel units are placed on shopping carts and are used to determine whether { TAIL ~ particular shopping carts } are authorized to exit { HEAD ~ a store }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD