I also have the Foy's Electronic Doorkeeper, mounted inside, with light sensor through the wall on the outside.
I LOVE IT.
The selling point was battery operation, and NOT a car, lawnmower or other 12v type battery hookup. (One of the options I found online used such, and the company owner replied to one of my e-mail inquiries with a rather derisive response when I asked about AAA or AAAA or C, or D batteries.)
But the Foy's automatic door is wonderful. Install it so the metal door slides past the bottom of the opening in the coop wall, so no critter claws can reach down to pull it up. The metal track keeps it tight enough so paws - or people hands! - cannot push it up, either.