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