Hi, I have several sliding glass doors on my home. After a couple of attempts to put the hidden door sensor 2845-222 under the latch, I finally came on a solution that works best. In my first two attempts I modified the hidden door sensor itself to force the hidden door sensor to fit under the latch of the sliding glass door. This was awkward and I really mutilated a couple of door sensors (one requiring superglue to hold it together).
In this last solution, I use a small loose lever arm. This has turned out to be the most reliable solution, working very well, so I thought I'd share it.
http://www.machomestore.com/catalog/pro ... cts_id=328
EDIT: A couple of additional thoughts.
If you make the lever arm just a little longer so that the loose screw holding it in place is accessible beneath the latch's extrusion plate, then when the battery dies in the hidden door sensor you will never have to remove the extrusion to replace the battery. You will only need to remove the lever arm and the hidden door sensor itself. The hidden door sensor has a low battery warning that gives you a heads up.
Finally, I cut my lever arm from the thick plastic white channel that they sell for installing 8x8 glass blocks (Owens Corning). Very suitable material, but almost any plastic will do. You could probably use metal or wood but wood splits and metal cuts like metal.