利用监视器可以帮助警察catch criminals, thus reducing crime. a camera is more effective than security guards. 警察和保安不可能全天24小时工作，而camera will not feel tired.而且它更objective, sometimes our eyes might deceive us, while a machine can exactly record what happens, it can prevent much unnecessary embarrassment. Frighten off the criminals and reduce potential crime.
Critiques about installation of surveillance typically look at the infringement of people’s privacy.
Being photographed and recorded by the camera,很多人feel uncomfortable and no privacy.特别是女性，有些人可能会将camera获得的资料用于illegal use.
3. 尽管有缺点，但是为了public safety ， 监视器是有必要的。但是应该尽可能balance the need for security with respect for individual’s privacy and freedom..