Wall-mount installation - mounts on the left or right side of door. No rails to hang, it simply mounts on the wall and attaches to the garage door torsion bar. Unit requires an electrical outlet within 6 feet. Patented absolute positioning technology - the newest technology in garage door openers. Liftmaster patented design allows the electronic limits to be extremely accurate, even after a power failure. Optional accessories: 475LM Battery Backup, 377lm Keyless Entry Pad, 379lm Fingerprint Keyless Entry,975lm Garage Door Parking Assist, 370lm Mini Remote. IMPORTANT NOTE: BEFORE PURCHASING, PLEASE VERIFY THE 3800 WILL FIT YOUR APPLICATION BY CONTACTING CHAMBERLAIN. TO RECEIVE IT AND THEN SHIP 33LB PACKAGE BACK TO SELLER IS INCONVENIENT.