Garage doors that close automatically have to have sensors that make the doors rise up again if the sensors detect anything in the path of the door. Sometimes these sensors go out of whack -- the individual parts aren't broken, but the two halves that sit at either end of the door become misaligned. If this happens once, you want to check the installation and ensure they were installed at the right spots on either side of the door. But if it keeps happening, and you're sure the sensors were installed correctly, there are a few other reasons to check out.
It's You (or Your Co-Workers or Customers)
One definite possibility is that you or another person who uses the space keeps brushing against one of the sensors and knocking it slightly out of alignment. If there is one particular sensor that keeps giving you trouble, and it's near a place where you normally walk, that could be the reason. Place brightly colored labels or tape near the sensor as a visual reminder to keep away. If customers bring pets with them, remind the customers to keep the pets away from the sensors.
Another possibility is a defective bracket that's allowing the sensor to become loose or to slide around. You may have to call a repair company to replace the bracket instead of doing it yourself, but this is a simple fix that shouldn't take long and shouldn't cost much. And if the door and sensors are newer, the repair may still be covered by a warranty.
Like any type of machinery or equipment, your garage door is subject to vibration. Excessive vibration from equipment around the door can gradually loosen bolts and screws. Those include the screws holding the sensors in place. If you have commercial equipment nearby, look into getting vibration damping systems installed, in addition to tightening and readjusting the door sensors. If you're sure that the brackets are being placed correctly, you may want to consider more permanent installation options that would basically cement the bolts or screws in place. You would still need to damp the vibrations from the other equipment, though -- at the very least, that will help stop other equipment from experiencing similar loosening problems.
Your garage door opener has those sensors for a reason, so you need them to work consistently. Luckily, those sensors are among the easier repairs to make. Contact a commercial door repair service for more help.