For those who can run juice to the coop, a $20.00 Safety First baby monitor is a great addition. Obvious limitations are obvious (no one at home to hear the growling/screaming of the chooks or, everyone is a heavy sleeper). We've had these monitors in coop and turkey shed for almost 8yrs. If the chooks start whining & growling or the turks start giving out with the worry hiss, it is time to put on the mudboots, grab spot and rifle and sneak out the door.
Have gotten very well trained, over time. The monitor receivers are on the head of bed and always cranked to max volume. Neither of us wakes up when the rooster starts crowing and the toms begin gobbling to greet the sun. However, Chook/turk `anxiety' `signals' will cause both of us to wake up.
Sometimes, in the summer (shed/coop windows open - double layer hardware cloth attached to frames with wood screws through oversized washers), I'll see nothing in general vicinity of runs/coop-shed, though a quick check of surrounding woods/understory/brush will reveal the eyes of the pred. (chooks/turks can often hear what is coming - through leaf clutter - at some distance) and that-is-that (if you live in woods and have a `regular' coon - always spotlight surrounding trees just after dark (if they aren't being `challenged' - they'll just sleep near the `chicken & rice bowl''') have taken out females and their broods, more than once, from big White Oaks/Hickories within 75yds of poultry (glowing eyes in the gloaming - easy shots).