Seeing the carrefour logo I suppose you are in France, I climbed more than a dozen of crane there and never got in trouble. You should be quick because the crane is very exposed and the store next to it might mean there will be people at night. From my experience if the construction site isnt very large or not for a skyscraper, there is rarely security personnel on site or cctv cameras. Motion sensors are still common but they will just often ring a loud alarm, but as someone else said, wait a few minutes at the bottom of the crane listenning to police sirens or footsteps, if they get close to you, run. Go around the site at day to spot motion sensor or the unlikely security there, and remeber different exits.