Sliding glass patio doors may be attractive to look at, but their weaknesses also make them attractive to burglars. Although these doors may have a bad reputation for failing to keep out intruders, their weaknesses are largely preventable and it's fairly simple to re-enforce a sliding door, and do it yourself.
Few sliding glass doors have locks on them when they're installed in the house. Most have only aluminum latches that can become worn or fall out of adjustment. Sometimes it's easier for the intruder to simply pry the door open at the latch or lift the door off the track than it is to break the glass.
To make matters worse, sliding glass doors are usually in the back of the property, out of view of neighbors and street traffic, which means the burglar has plenty of privacy to do his "work." Warm weather makes it even easier for burglars because so many people leave their sliding glass door open for air circulation or so that pets can go in out.
Since these glass patio doors slide horizontally, it is important to have a blocking device in place in the track to prevent the door from being fully opened from the outside. The track-blocker should allow the door to be opened up six inches, but no more. All you really need to do is place a strong wooden dowel or metal rod into the track so the door can't be slid open. A more serious option is the "Charley Bar", a metal bar that attaches to the doorframe and extends to the edge of the sliding part of the door. When not in use, the bar folds up and out of the way against the frame. There are also track-blocking devices that can be screwed into place.
Even if you use a blocking device, it won't keep out the more determined burglars who may simply lift out the entire door. One of the simplest ways to prevent lifting is to keep the door rollers in good condition. When the rollers are in proper working order it's harder to pry the sliding panel up out of the track. You can also install an anti-lift device such as a pin that extends through both the sliding part and the fixed part of the door.
A simple do-it-yourself way to prevent lifting is to install screws at the top of the sliding glass doorframe. This will let you open and close the door as usual, but will prevent anyone from lifting the door out of the track.
Drive 1-1/2-inch pan head (large head) screws into the top of the doorframe spaces about every 8" or at both ends and in the middle. Drive them so their heads just clear the top of the door. For metal doorframes, use self-tapping screws (the ones usually used for sheet metal and plastic).
Sliding Door Locks and Alarms
The most effective method of locking a sliding glass door is a sliding bolt with a locking device. For the best security, chose a sliding bolt lock that can also be padlocked. There are also models of sliding door locks that sound an alarm when the door is opened.
The cheapest way to dissuade would-be thieves is to place an "alarm system in use" or "beware of dog" decal on the sliding glass door near the handle. Since the effect is merely psychological, these decals shouldn't be used long-term in place of blocking or anti-lift devices, but if you've just moved into a new place, it's a good temporary solution for keeping your sliding glass patio door secure.