Good question, So I have decided to write about this today.
There are good reasons to install a lock. This week I have had to fix two swing motors of different brands because the gearbox is destroyed because someone decided to just force the gate open because they didn't have a key or remote.. You need to think about this, you might have a farm gate that is 4.3m long. At one end of the gate you have a swing motor maybe about 1m long connected to a solid post and the gate. The gate is like a giant lever against a 1m long motorised ram and if you decide to push the gate then something needs to let go. Sometimes it is the brackets that bend or the screws come out of the post. Some times the gate hinges let go or bend. But mostly the swing arm with a smallish gearbox inside will take most of the force and destroy itself. Either the motor shaft will break or the gears inside the housing will strip, and let go just so you can open the gate. Sometimes you can fix them but mostly not.
A new swing arm can be between $300 - $500. not a small sum but what if you had a lock, either a magnetic lock or an electric lock... then you are protected and no one can force the gate at all.. Problem solved.
If you have an electric gate system then go for a magnetic lock. These are the best for swing farm gates because there is always a bit of bounce or movement in a mesh farm gate and a magnetic lock does not care and it will lock easily as long as the two halves of the lock get close enough, but if you have a solar system then you would need an electric lock. These have a small window for the two halves of the lock to connect and if the gate sags over time then the lock position would need to be checked so the lock does not jamb on closing.. Most control boards have a connection for an electric lock but only a few have a connection for a magnetic lock so you need to check that.
Both lock systems are easy to fit yourself but just check that your brand of controller can take an electric lock or magnetic lock or both..cheers Graeme