Not just "eavesdrop on workers". Also "eavesdrop on customers". The patent itself tells us:
"the sound sensors can capture sounds resulting from guests talking while waiting in line at a terminal or any other sounds resulting from the presence of guest ... the sound sensors can capture audio of conversations between guests and an employee stationed at the terminal. The system can process the audio of the conversations to determine whether the employee stationed at the terminal is greeting guests."
"the sound sensors can capture sounds resulting from guests talking while waiting in line at a terminal or any other sounds resulting from the presence of guest ... the sound sensors can capture audio of conversations between guests and an employee stationed at the terminal. The system can process the audio of the conversations to determine whether the employee stationed at the terminal is greeting guests."
http://pdfpiw.uspto.gov/.piw?docid=10020004&SectionNum=1&IDK...