Largely because of controlled frequency assignments, it is often very simple for criminals to determine the police frequency band and monitor it. By using radio direction-finding techniques, the criminal operative can locate and track fixed, mobile, or portable transmitters. A skilled intercept operative can acquire a wealth of information about a police agency, its operations, and personnel after only a few days. Patrol patterns, shift command structures, undercover operations, or staging areas for raids are only a few of the types of information that can be gained with relative ease. Mobile telephone systems also can provide a wealth of sensitive information to operatives. Finally, because of the large amount of time they spend on the air, dispatchers may be the most prolific source of information for operatives. Because of the potential vulnerability of police communications, it is vital that communication security surveys be conducted to determine deficiencies in equipment, personnel, or procedures that could permit unauthorized access to confidential information during transmission.