Keeping track of people is a big part of what the FBI does. Doing this in a way that doesn't alert the person who is being observed is critical, or she may attempt to escape. The FBI uses a wide variety of surveillance techniques to gather information without being detected.
FBI agents may follow a person of interest as that person leaves and returns to his home and goes about his daily business. This is done by using a team of people who alternate with each other to avoid alerting the person who is being followed of what they are doing. Agents may be any age, race or gender, and dress in ways that help them to blend in with crowds. The purpose of personal surveillance is to gather information about a person's activities, destinations, contacts and schedules.
Vehicle surveillance is done for the same purposes as personal surveillance, but uses one or more cars to keep track of a subject who is also in a car. The FBI has developed sophisticated methods of vehicle surveillance that involve cars that may be behind, in front of or even on parallel streets with the subject's car. Agents communicate with each other through the use of hands-free radios, allowing them to speak without the possibility of alerting someone who is watching them in their cars.
Electronic surveillance includes phone taps and hidden microphones that are placed in residences, in offices and even on people. Hidden microphones are extremely small and can be concealed behind pictures, inside of appliances and on clothing. The FBI also has microphones that can eavesdrop on conversations within a building from outside the building. These directional microphones use extremely high frequency waves that are focused on a window, measuring the vibration of the window glass that results from a person's voice and translating it back into speech.
The FBI has kept up with the development of the Internet and online technologies, and uses sophisticated methods of surveillance to track how people of interest are using online communications. These methods include things such as viruses that can be sent through email, infect a target computer, and then allow the FBI to track the keystrokes on that computer. ISPs can track many forms of communication that people believe are anonymous.