What is a photocell. What are they and why do I need one

Why a photocell. What are they and why do I need them?. Well you don't really but most people that install sliding gates do like to install them. So what are they...A photo cell is a light that is sent across the gate way to a receiver or reflector on the other side.  The idea is, if the light beam is broken, ie a person standing or a car stops in the gateway,  the motor will stop so nothing gets hurt.across the gate so if anyone or anything is across the gate, the gate motor will stop or not work at all.  Sliding gates are worse than swing gates because the gate is on a track and it can slam into the side if a car or trailer should stop across the gate. So for those that want a slide gate, is is probably a good thing to do. Swing gates can work the same way with a photocell, but as you can imagine, the photocell can only go on one side because the other side, the gates will be in the way of the photo beam, so it will stop the motors when the gates open. The other way is to install the photo beam away from where the gates would be when fully open but that won't work if someone is closer to the gates than the beam. 

The other issue with photo beams is reliability. We get a lot of calls from gate owners saying the gates don't work any more. A great deal of the time the photo beam has moved so it won't line up with the receiver on the other side, or the photo beam has stopped working, or even the beam has water in it so it won't see the light beam from the other side. So what I am saying here, yes good for safety but more issues when faulty and nothing will work if the beams are not right. I say, the more things you add to your gates, , the more things to go wrong.