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With the exception of at large buildings in dense city centers, just about everywhere else, utilities enter a building at just some point on the back, out in the open. This includes utilities that feed alarms and security cameras.
While some places will have systems in place for situations where these outside connections have been severed, like independently operated cameras on an intranet, cellular data backup for alarms, electrical generators, etc., most places don't, so successfully circumventing their security is just a matter of cutting all the cables on the back of their building at the same time, and then being gone before they notice
I'm not an expert on modern alarm systems but it seems that it is very common and fairly inexpensive to have cellular data backup. Not every system has it, but many do. In that case cutting the main connection will likely result in someone appearing on site fairly quickly.
Many cameras also have some form of local buffering. So even if you are gone before someone does show up you still may find yourself recorded.
But at the end of the day just put a bag over your head and you can be gone by the time anyone shows up without leaving a meaningful trace. Other than the very top-end system security systems just keep the honest people honest.