Garage door remote controls have a range of about 25 feet under normal conditions. They operate using radio frequencies. The remote control you keep in your car transmits a signal to a receiver at or adjacent to the door opener motor. Unlike a television remote control that uses visual infrared signals, garage door opener remote controls can transmit and receive through some obstructions.
Replace the battery or batteries in the remote control. The batteries provide the power to send the signal; a lower voltage in the battery will reduce the garage door opener's range.
Remove obstructions between the remote control and the door. While garage door opener remote controls are more tolerant than television remotes, they won't transmit through heavy metals, such as lead. Other problem obstructions can include concrete with rebar.
Adjust the antenna on the garage door opener motor. It's often just a little piece of wire hanging down. Like the FM antenna you have on a radio, it can benefit from being wiggled a bit. Change the angle and try the opener again.
Reposition the remote control in the car. Avoid pressing the button when the remote control is down on the floor when you are at the fringes of range. The remote has to penetrate the engine block to reach the receiver.
Some installations will have a shorter range because of metal siding on the garage or reflective coatings on the door.