What does this product do exactly? I use a storage unit that has a gate around the group of storage units it is part of. You put a code in and the gate opens and it closes on its own after a time period. It has one of these devices on one end of the gate and I wondered what it's function was. Today my friend was driving out of the gate, stopped briefly (not more than 10-15 seconds for traffic going by, and the door started and the fence door. The fence ended up hitting my friends. So I'm wondering ,gate ⁸