I'm sure glad I found this thread. Thanks to those who posted examples, and educated me about the alarm call.
I just came in from closing the girls' door... Boy oh boy what an evening ordeal. We're chicken-sitting three stranger hens and tonight is the first night. I put them up in a separate cage, but put the cage in the coop. My roo deemed them enemy hens-of-doom-and-danger and sounded the alarm (which I thought was the egg song, too from watching youtube videos!), he wouldn't let any of HIS hens in to roost in the coop. Then several of my hens joined in the alarm/egg song, which I had never heard them do since none are laying yet.
I was really surprised, because I have been waiting, waiting, waiting to hear the egg song (my girls are all 5 months old today, no layers yet). And finally I hear them sing it, and they're all just flipping out over stranger-danger. Harumph...
I ended up having to move the cage full of strange hens to the shop. Then it took me another 30 minutes in the almost-dark to convince my birds the coop was safe, collect those who decided trees would do for a substitute bed, and find my poor white polish hen who got lost in the kerfuffle and was roosting 100 feet away on a roll of fencing wire.