This is what it looks like when you screen a nest at night. You may click on the photo for more detail.
Before dark, a ranger or volunteer will head out to nests where activity is being heard and hatchlings are close to emerging. A screen is placed over the location of the egg chamber and sand is built up around it. This keeps the crabs out and also confines the tiny hatchlings should they emerge when no one is there (and possibly become disoriented).
Someone will patrol the nests during the night to check the progress.