A more thorough explanation:

Fixed surveillance

Fixed surveillance is when an investigator watches suspects in-person from a distance to gather evidence. This is different from electronic surveillance, which uses technology to monitor people.

Another name for fixed surveillance is a "stakeout."

An investigator might conduct fixed surveillance on a suspected drug dealer. They would park their car near the dealer's house and watch for any suspicious activity. They might take pictures or videos to use as evidence.

Another example is an investigator watching a cheating spouse. They might follow the spouse to see if they are meeting with someone else.

These examples show how an investigator can gather evidence by physically watching suspects. Fixed surveillance can be time-consuming and requires patience, but it can provide valuable information for a case.