just insert USB inside car ,
as soon as car comes near to gate , automatic door will open. ( either using sliding gate motor or boom barrier or gate opener arm, or swing gate motor , whatever way is being used to open gate by electronics means) 
receiver need to fix to motor circuit, or boom barrier circuit or gate opener circuit.
1 receiver can add up to 340 USB transmtter . so you may add 340 cars to 1 reciver.
box contain
1 receiver 
1 USB transmitter.

for exta USB refer other listing
see video operation
youtube.com

Works with any garage or gate opener system. If you unable to find remote control to match your gate or door opener system, you can easily solve this problem purchasing this kit. This receiver is universal and works with any gate or garage door system.
Just connect it in parallel according to the manual diagram and the garage door opening system will work with your existing garage door opener control board.
Hands Free: Connect by Bluetooth,no remote or phone needed.
When people drive their car with USB plug inserted into the usb charging port , the door will be open automatically within 10 meters. The door will close automatically after the car entering into the gate if the gate motor has automatic close function.