Product: Liftmaster LA500PKGU 24VDC Residential/Light Commercial Single Gate Opener Kit, Battery Backup, Receiver & Photocell Included!
Brand: FAS
LA500DC Primary Arm is a replacement arm for the LA500 system. It will move a gate that is either 18ft or weighing up to 1200 pounds. It will open up to 90 degrees in 15-17 seconds. Before you purchase make sure that you need to the primary arm and not the secondary arm. 
The primary arm will not work as a secondary arm 

MyQ Technology Provides the ability to remotely monitor and activate our gate from anywhere in the world via an Internet-enabled Smartphone or computer.
Battery Backup System provides uninterrupted access when the power is out Provides up to 14 days or 500 cycles on battery backup. Also powers safety and ancillary devices.
Security+ 2.0 Technology Our patented Security+ 2.0 Technology provides two times the range of standard remote controls and virtually eliminates radio interference. An on-board radio receiver is included with the LA500. It holds up to 50 remotes and is compatible with HomeLink version 4 and higher

Search query: lift master driveway gate sensor
Relevance: Exact