The police are now monitoring criminal/gang/drug 'activity' in the area.
There has been an increase in the city's (level of) economic 'activity'.
The instruments are used to detect volcanic 'activity' on the island.
(..) ...our hearts tell us there is something else out there. I know what I saw. Tell me what I'm supposed to believe. I'm a member of a secret organization that monitors alien activity on Earth. Ben was an alien. So were his killers. I don't know why they did it, but I promise I'm gonna find out. Okay. (..)2002 Men in Black II