Surveillance/sɜːrˈveɪləns/ Definition 1 of 4Pro Tip 1/3Crime Prevention Surveillance is used to deter crime by making people feel they're being watched. The presence of surveillance cameras can make thieves think twice. Pro Tip 2/3Not Always Visible Surveillance can be covert, meaning you might not see cameras or guards. Hidden surveillance devices could be listening in. Pro Tip 3/3Public Spaces Surveillance is common in areas with higher security needs like airports. You are under surveillance when you pass through airport security.