I purchased the very pricey McMurray Automatic Coop Door shortly after I bought my coop. DO NOT SPEND YOUR HARD EARNED MONEY ON THIS PIECE OF JUNK! It has a terrible design, utilizing a string pulley system that attaches to a spool. The spool has a notch in it where you insert a knot at the end of the string. It doesn't work. It is supposed to sense the tension on the string, but lord help you if the string isn't just perfect. The knot won't stay in the slot... the spool keeps winding and you can hear the motor groan... or it gets tangled up... its just a nightmare. I tried to use it for a few weeks but just gave up, because I got tired of climbing into the coop to try to fix it every day. Its easier to just open and close the door myself.