French doors are difficult to secure for several reasons involving the following weak spots.
Securing wooden french doors.
The best french door security will have a 3 point locking system.
The fixed door on many french doors is held closed by a pair of barrel bolts that sink into the top jamb and threshold of the doorway.
This alone will make it a lot more difficult for a burglar to force the doors open.
Out of all the locking options to secure a french door a single sided deadbolt is the best option.
When french doors open outward the hinges are exposed on the outside.
Even if these are tight enough to prevent the fixed door from.
This means anyone can remove the pins and take the doors off the hinges.
Three point locking mechanisms are best for french doors.
For doors that come as a pair consider locking securing one of them permanently.
Install a commercial grade double sided deadbolt into the active side of the door or alternatively install a double side high security deadbolt into the active side of the french door.
Because french doors have no center frame or support they are very weak in the center.
Traditional wood french doors have many small panes of glass.
For doors with a bolt that slides to lock along the top and bottom of the door you can permanently lock the door by drilling a hole into.