You could have downloaded ShadowBook 1.1 for Mac from our application library for free. The application is included in System Tools. This free Mac app is a product of Medallia.
From the developer:
The application will trigger if the left sensor value is below the threshold, and the right sensor is above. Due to what appears to be a hardware bug the right sensor cannot be used a trigger. This program can send a notification to make it switch to the next desktop
You may want to check out more Mac applications, such as iPAD or Bulldog, which might be similar to ShadowBook.