I use a Fisher Price monitor that I got cheap at a yard sale. It only relays sound, not video, but for $3 I'm thrilled.
I had it in the brooder and it moved out to the coop with them. I lock them in securely at night but I have heard coyotes right outside the coop through the monitor. Immediately took my dog out to investigate and she verified that at least 2 had been smelling around the foundation.
Now I listen to them instead of a radio because I enjoy their chatter; it is so pleasant. I can see the run from my window and hear them as if they were right under it. It picks up both the coop and the run. I have it on all night, of course, and it does not interfere with my sleep.
They are close to laying so I am listening for that, too.
I totally love my monitor!