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Check your sliding glass door to see if it has an actual lock on it. Sliding glass doors usually do not have locks on them, only latches. These latches are usually made from soft aluminum or cast metal, and quite often become worn or out of adjustment. Because of their location (usually at the rear of the home) and the many inadequate latching mechanisms on the market, sliding glass doors usually offer little resistance against physical attack. This, combined with the wear and tear factor, makes these doors a prime candidate for a break and enter.
In warmer weather, sliding glass doors are often left open to allow ventilation or pet access. Unfortunately, complacency often results in an opportunity for a burglar to take advantage of an open door. This doesn't mean that we have to spend all spring and summer with our sliding glass doors locked up tighter than a drum. It simply means that we have to take a few precautions to ensure that we keep the intruders away.
This can be easily accomplished by inserting a wooden dowel or stick into the track. It is important that the wooden dowel runs the whole length of the track preventing or limiting movement of the door. If your sliding glass door slides on the outside, place the wooden dowel between the handle and the stationary part of the sliding door ensuring limited movement.
There are various other blocking devices available that fold down and prevent the door from being pried open. These devices are called "Charley Bars" and are available through several manufacturers.
Door ventilation can be addressed by installing a sliding door lock on the stationary part of the door at the bottom track. This metal lock will bolt into the moving door and prevent an intruder from prying the door open. A second hole can now be drilled into the moving door at a desired location to allow the door to remain locked in the open position.
Make sure that the sliding patio door lock has the ability to be locked with a key to prevent an intruder from opening the lock from the inside. Always keep a key close by in case of fire.
To prevent lifting the door out of the track, you need to keep the door rollers in good condition and properly adjusted. Installing self-tapping screws in the door's upper track is also crucial. Once the screws are installed, open and shut the door through its entire range. There should be just enough of the screw's head protruding to allow free movement without allowing the door to be removed.