Spying or surveillance is not only for spies. It is very important to understand that  surveillance  is done in quite a lot of fields. Quite often, there are very specialized kinds of surveillance equipment being used for some very unique purposes. Quite a number of unique fields will require unique surveillance instrument to perform functions that would not normally be done by people in other areas of expertise. Volcanologists will for example, use seismographs. However what most people will need will usually be video cameras that could be controlled from a remote station.