Yes, I have a night-vision baby monitor. Primarily useful at night, since they spend most days when I'm home free-ranging. Definitely puts your mind at ease knowing you'll be able to hear any predator attacks and intervene. We run an outdoor extension cord out to the coop, since we don't have power there.
It's a Summer Infant Day and Night Color Video Monitor, and I think it cost about $150.
(It's only color in daylight. At night when the IR kicks in, it's black and white.)