Shoplifting may be prevented and detected. Closed-circuit television (CCTV) monitoring is an important anti-shoplifting technology. Electronic article surveillance (EAS) is another method of inventory protection. Radio-frequency identification (RFID) is an anti-employee-theft and anti-shoplifting technology used in retailers such as Walmart, which already heavily use RFID technology for inventory purposes. Loss prevention personnel can consist of both uniformed officers and plain-clothed store detectives. Large department stores will use both and smaller stores will use one or the other depending on their shrink strategy. Store detectives will patrol the store acting as if they are real shoppers. Physical measures include implementing a one-way entry and exit system, protected with devices such as "shark teeth" gates to ensure trolleys can only pass through one way.