Homelink is a standard for wireless remote activation. It is usually used to remotely open garage doors and gates. Most modern vehicles include a homelink remote in the car somewhere (either as an option, standard equipment, or OEM addition).
As you approach your gate, you press one of three homelink buttons, and the gate conveniently opens to allow your vehicle in. The problem is one of range. When you press the button it often works for only a second or so - if the homelink receiver is not in range, the gate will not open, and you need to drive closer before trying again.