Can CCTV work without internet?

Yes, CCTV can work without internet, and traditional CCTV systems were designed to work without internet long before internet existed. Analog CCTV cameras connected to DVR via coaxial cable and power cable work completely offline, recording video to local hard drive in DVR, and you can view footage on monitor connected to DVR without any internet connection, internet is only needed if you want remote viewing on phone. Similarly, IP camera systems with NVR can work on local network without internet, cameras connect to NVR via Ethernet cables or WiFi router, NVR records to local hard drive, and you can view on local network, internet only needed for remote access from outside. Even wireless cameras can work with local WiFi without internet if router is on, though many cloud based cameras require internet to function because they record to cloud not local. Benefits of offline CCTV include no internet bandwidth usage, no reliance on cloud subscription, and less hacking risk from internet. Downsides include no remote alerts and you must be on site to view footage. So if your internet goes down, your CCTV will continue recording locally, you just cannot view it remotely until internet returns.