Roosters don't crow just for the heck of it -- ask yourself *why* he's crowing at night, you might be surprised, and then possibly alarmed!
I live next to my folks and the chicken house is actually in their backyard. There are times when I go between the house at night, and if no one's walking with me I'll often talk on the cell phone to my Mom in the kitchen. THIS sets Rooster off because it's not usual and it's upsetting. He calls until I tell him who I am. I suspect he also calls if someone comes in late, and I know the garage door upsets him.
During the day he alarms at people in my front yard (but not Mom and Dad's... go figure. Maybe he can't see as well up there). He alarms at the dog. Every crow has a reason -- maybe not an obvious reason for a person, but certainly one for a chicken. I'm sure he crows at night when the deer come through, and I have no doubt that he'd alarm if something tried to get in the coop at night.
He thinks he's doing his job; yours probably does too.