Hey Folks,
Just got my SmartThings hub and sensors and was profoundly disappointed to realize that there are essentially no outdoor motion sensors.
How can this be?
I tried the obvious thing of pointed an indoor sensor at the front yard through my living room window. It seems that the glass stops the sensor from working. Is there a workaround for this? Why do the sensors not work through glass anyway?
Most motion sensors detect changes in Infrared Radiation (like from a human entering their field of view). Glass is opaque in the IR portion of the spectrum, so motion sensors can’t detect changes outside.
IR sensors outside are very unreliable because the environment is constantly changing. You’ll get lots of false motion events.
Most folks who need outdoor motion detection use cameras or laser trip sensors.
There are plenty of options for outdoor sensors and they will almost certainly perform better than a standard ST motion sensor placed outside.
Have look here:
Hi, i have been searching for something like that, so far no success.
Laser trip sensors? like what?
Just use the link in the post above yours for the outdoor motion sensor FAQ and you will find detailed discussion of trip beam models and various other options. 
Microwave motion sensors maybe???