What are the range of the sensors? How far away can I put them? What about walls?

The WisDom sensors, keypads, and keyfobs are rated for approximately 1,000 feet line-of-sight (meaning with nothing in the way). 

When it comes to transmitting through walls, these sensors perform very well in normal domestic environments.  It is impossible to analyze what effect particular physical structures and/or building materials may or may not have on wireless transmission without actually testing the equipment in that precise scenario.  In the unlikely event that you run into a transmission problem, there is a repeater that you can get for the WisDom system that will help you to bridge a connection between the sensor signal and the panel.

The nice thing about the WisDom is that it is technologically advanced enough to be able to tell you (via a numerical rating) how strong the signal is from each sensor, so that you can choose the optimal location for each sensor and not have to worry about signal strength.