Most CCTV Systems can be remotely monitored over the internet and viewed on a computer or smart phone.
Professionally monitored systems normally work in conjunction with detection devices. The remote monitoring centre is alerted and can view the the camera images from the site. If intruders are present the operator might have the option to speak into a microphone and warn them off. Depending on circumstances, the operator can contact a key holder who can attend the site and where the system is configured to do so, notify the police.
Where sites are not enclosed (such as car sales area), remotely monitored CCTV is often the only option.