Rather than using a catch or bolt for locking swinging driveway gates manually, automatic swing gates are locked to some degree by the motors that open and close them, although if a gate is wider than 2m (6 1/2') or the opening angle is more than 110o the slop in the hinges and flex in the gate may allow it to be pried open a little putting undue stress on the motor and it maybe enough for someone to squeeze through, so an electrically operated lock should be used that is released (unlocked) by the automatic gate operator when the gate is opened.  

Using Hard Stops 

If a gate motor closes the gate up against hard stops the slop in the hinges is taken up and the gate becomes firmer so an electric lock may not be needed, although with double swing gates this means having a stop in the middle of the driveway, which can be a trip hazard for pedestrians or if high enough can catch the bottom of a low set vehicle. To minimise this, a cast aluminium stop plate is available that that sits only 35mm ( 1 6/16") above the ground and has no sharp edges.  Ideally a gate has at least a 50mm (2") gap under it so normally would have extensions that come down to the stop plate.

If hard stops are required for the open position a simple rubber door stop can be used if the gate opens up against a fence or wall otherwise a small post with a rubber stopper on it could also be used.  

Rather Not have a Stop Plate in the middle of the driveway? 

If the gate motors don't require hard stops on the gate (some do) and you'd prefer not to have a stop plate in the middle of the driveway for your double swing gate then a good technique is to make sure one side closes first and stops a little short, then the other side, which is fitted with a stop plate will close against the first and pull it that last little bit to the fully closed position taking up all the slop from the hinges, making the gate nice and firm and making sure that both gates close inline.

Using a Magnetic Lock

From our experience the most effective way to electrically lock a swinging driveway gate is a magnetic lock that locks a single gate against a receiving post or for double gates locking them together or to the ground. A magnetic Lock is basically an electrically powered magnet that holds onto a steel holding plate whenever 12VDC or 24VDC power is applied to it. When this power is removed it is no longer a magnet so releases its hold. The holding force of most magnetic locks is at least 200kg if installed correctly.

It is important to install the holding plate correctly so it has an amount of pivotal movement so when coming in contact with the magnet it aligns itself to fit exactly on the magnets surface so will hold with full force.  If the holding plate is too rigid then it will contact the magnet only in one small spot and its holding ability will be significantly reduced. 

The advantage of a Magnetic Lock over other type of electric gate locks is if the gate drops at all because of wear and tear in hinges or the gate post moves out of plumb due to ground movement the lock cannot jam up or loose contact.  The ground can move with variations in moisture and temperature or if there are any trees growing near gate posts their roots can move the post as they grow bigger over time.  The disadvantage of a magnetic lock is they do draw power to lock, not a lot, but generally too much for a Solar Power Gate Operator and can cause the battery to run flat over night, making them unsuitable for Solar Powered Gates.

Normally when fitting a magnetic lock to a single gate a 'Z' shaped mounting bracket is used for the lock on the gate that contacts a flat steel holding plate fitted to a receiving post.  Power for the lock is run from the control unit of the gate operator to the gate hinge where there is a power transfer device that takes it from the post to the gate safely and then inside the gate frame to the lock.

The holding plate is normally fitted to a small post set inside the main post if the post is wide and the gate is to go in the middle of the post or can go directly onto a narrow steel post if the back of the gate is flush with the back of the post.  For double gates the lock is on one side and holding plate on the other so the gates lock together.  The side with the holding plate must close first followed by the side with the lock.  By locking double gates to together there will still be some movement of the gate if someone grabs it in the middle and pulls or pushes but they won't be able to pry to two sides apart because the lock is holding them together and there won't be any stop plate in the middle of the driveway.

With single swing gates the magnetic lock may also be fitted to the post and the striker plate on the gate with the cable run across the driveway if this is easier.  Sometimes cable is required for other devices across the driveway so adding a lock cable to this would be easier than running it in the gate itself.

Magnetic Locking to the Ground for larger Double Swing Gates 

By locking both sides of a double swing gate to the ground, if someone grabs the gate and pulls or pushes it, it will be firmly locked.  This will require a hard stop in the middle of the driveway and the Magnetic Lock fitted horizontally under the gate facing towards the road.  The hard stop can be made using a length of 50mm (2") metal square hollow section with its ends cut at 45o so a vehicle can drive over it without puncturing tyres. The side without the magnetic lock closes first and stops against a hard stop in the middle of the driveway then the side with the lock closes over it, locking them both in place.

To further reduce the intrusiveness of the hard stop a mound of concrete can be formed on the street side. With the average width of driveway a car or truck would never drive over the ground plate anyway, although motor bikes and bicycles could and pedestrians using the gate can trip on it.

Using an Electric Strike Lock

Strike locks are preferred for Solar Powered Swing Gates because they don't draw power all the time which can run the battery flat over night. Strike locks only require power for a short time to release the lock. The issue with electric strike locks is if the gate drops at all because of wear and tear in hinges or the gate post moves out of plumb due to ground movement the lock can jam up or loose contact. The ground can move with variations in moisture and temperature or if there are any trees growing near gate posts their roots can move the post as they grow bigger over time. Because of this the posts must be metal with thick walls so they don't flex much and be concreted into a reinforced concrete footing that runs between the gate posts so the whole gate structure becomes one and ground movement will have little effect.  The strike plate must also allow for vertical movement of a single swing gate.

Another issue with electric strike locks is if the the gate has some wind on it or other force that is putting pressure on the tongue of the strike lock it can bind and not release so the gate operator should push the gate against a hard stop to prevent this from happening, so when using an electric strike lock you cannot do so without using hard stops.

Electric Strike Lock for Single Swing Gates

These are fitted horizontally with the lock fitted to the gate and strike plate fitted to the post. Cabling for power the lock would normally be installed inside the gate frame if it is hollow and must be flexible as it will need to be run to the gate posts and to where ever the control box is for the automatic gate operator.   

Its important with electric Strike Locks that when the gate is closed there is no pressure on the tongue from the hard stop other wise the lock may not work properly, although locks with a rotating bolt minimise this  So it must be aligned carefully so when closed there is at least a 1mm gap or so between the tongue or the latch and the strike plate/lock. 

Electric Strike Lock for Double Swing Gates

These are fitted vertically on one side and each gate must have a hard stop fitted and the side with the lock closes over the side without the lock so it is locked too.

Wiring up Electric Locks

Different brands of gate operators have different outputs for electric locks, not all of them are so easy to connect a magnetic lock.  The easiest is an operator that has a 'Clean Contact Lock Output' and either a 12VDC or 24VDC auxiliary power output.  The magnetic lock voltage must match that of the auxiliary  output.  Most lock outputs provide 12VDC for a short period when the gate is opened.  This is ideal for electric strike locks (even 12VAC locks) as all they need is a short pulse of power and the lock is released and the gate can start moving even once there is no longer power applied to the lock. With magnetic locks however there needs to be power on the lock to lock it and power must be removed long enough for the gate to start opening so the magnetic lock is no longer touching its holding plate.  If it is then the gate won't open because the lock is still holding it closed.

If the operator outputs a short pulse of voltage for a strike lock only (like the King Operators do) then an interfacing relay is needed for a magnetic lock, wired so it provides the power to lock the gate and removes it to release it.  If the lock output doesn't hold on long enough then a timer relay should be used that will hold it for a preset time OR use the light output if it has one.