Securing your sliding glass door (patio door) is a must: Thieves target sliding glass doors because they're easy to force open even if the conventional lock is engaged. The key to securing sliding glass doors is to install a mechanism that prevents an intruder from forcing the door to slide or to lift.
First, make sure that the existing door lock works. If it doesn’t work, home centers carry replacement locks.
Prevent the door from sliding open by buying a locking device that blocks the track. Or create your own device by cutting a length of wood (such as a broomstick or a 2-x-2-inch board) to fit snugly between the doorframe and the stile of the operable door.
Make this feature even more secure by drilling a hole through one door and into the other. Then insert a long nail or bolt through the holes; this prevent intruders from prying the door up and swinging out its bottom to gain entry.
To prevent someone from breaking the glass to get in, install a tough window film (sold at local glass installers). This film prevents the glass from shattering and resists forced entry.
