Surveillance means using a device to watch over a person or persons at work. That device might be:
- a data surveillance device, i.e. monitoring input or output of information into or from a computer;
- a listening device, i.e. monitoring conversations or words spoken between two or more persons;
- an optical surveillance device, i.e. recording vision or observing an activity, e.g. CCTV; or
- a tracking device, i.e. determining the geographical location of a person, e.g. GPS.