{TAIL ~ A detector} at the entrance of a defined area detects passage of {HEAD ~ a customer} at the entrance 
{ TAIL ~ A detector } at the entrance of a defined area detects passage of { HEAD ~ a customer } at the entrance
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH