Other forms: surveillances
Many times, a person suspected of something illegal by the authorities is placed under surveillance, meaning he or she is closely watched to see if their suspicions are well-founded.
If you break down the word surveillance you get the prefix sur, from the French word for "over" and the root veiller, meaning "to watch." All of which is a roundabout way of saying that if you are under surveillance, you are being closely watched — usually by the authorities, and usually not for a good reason! Those surveillance cameras in banks and stores are put there in the hopes of both preventing crimes and recognizing criminals after a crime has been committed.