“That which does not kill us makes us stronger.” ― Friedrich Nietzsche

During a criminal investigation, private investigators might use a number of surveillance options to gather the information and evidence they need. Here is an overview of the four most common forms of surveillance in criminal investigations.

1. Stakeout – Also called fixed surveillance, a stakeout is when a PI or a team of them observes a person or location for a period of time from a distance, documenting activity and collecting information about the suspect or location. Often, PIs will work in teams of two or three for stakeouts to be able to relieve each other and to switch positions to lessen the possibility of being noticed and blowing their cover.

2. Unmanned Surveillance – This is also called fixed or stationary technical surveillance. With this type of surveillance, a parked car is set up with cameras and recording devices to record the activity of a location. This type of surveillance helps avoid investigators being noticed and allows surveillance teams to come and go to check or change out equipment when they have lower chances of being recognized. It also gives them the ability to monitor a location around the clock.

3. Wiretapping – Also known as electronic monitoring, wiretapping includes surveillance of someone’s phone, email, fax and internet. Wiretapping generally requires a court order and is most often used in criminal cases involving organized crime or issues of national security. This type of surveillance can also include the use of drones, computer forensics, license plate readers, facial recognition technology using a person’s devices and subpoena of data stored in the cloud.

4. Undercover Operations – Undercover operations involve the investigator playing an active role in witnessing, monitoring and revealing criminal activities. In these cases, the investigator infiltrates and gains the trust of the person or organization under investigation. This is often the most dangerous but also least common form of surveillance in criminal investigations.

During a criminal investigation, private investigators must use a variety of methods to gain information and evidence for a case. Surveillance is just one of those methods. These four common forms of surveillance are those most commonly used by private investigators to get the information they need to prove or solve a case.