Out of all the locking options to secure a french door a single sided deadbolt is the best option.
Securing french door from inside.
The purpose of multi point locks is to secure the door at.
To do this we.
Install a concealed lock for french doors.
This alone will make it a lot more difficult for a burglar to force the doors open.
However a deadbolt that locks both doors together and single sided deadbolts in the top and bottom of both doors are a good combination for securing both doors.
Add one side half deadbolts to the top and bottom of each door.
Use a door barricade.
My absolutely favorite method is the nightlock security door barricade from amazon.
How to secure french doors from burglars.
Traditional wood french doors have many small panes of glass.
Alternatively glue and screw a stop on the inside edge of the fixed door.
This means anyone can remove the pins and take the doors off the hinges.
French doors are difficult to secure for several reasons involving the following weak spots.
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.
When french doors open outward the hinges are exposed on the outside.
The best french door security will have a 3 point locking system.