I now have them locked up and I will place IR sensors in front of the coop and towards the garden. I will attach that to a doorbell, and when I hear "the call", I'll go check on them. I'll make sure small animals won't trigger it. It's not the only time We've seen someone lurking around under cover of darkness. Once, we've seen footprints in a fresh concrete we've made in the evening and then we've been arguing about who was stupid enough to walk bare-foot in there - yes, the idiot was bare foot to make less noise (that was summer, now windows are closed and we hear nothing...). Several times my dogs barked for no apparent reason during the night, and one time, I took them out at 3 am in the morning, when we got lie 50 meters away from the house, they started growling and ran towards a guy that was snooping around. They chased him several hundred meters and he must have broke the speed record. I could see him because of full moon, otherwise, I'd just call my dogs back when they started.
Could be the same guy. Perhaps he likes to get free stuff during the night. I don't know.. He was young, quite tall and in fit condition. At least the one my dogs chased. When I get the alarm thing going, they will get their chance again. After a couple of treatments, I doubt the asshole will return.