WaterSwitch used for Residential Systems by Irrometer - Includes one sensor.

WATERSWITCH by Irrometer

Designed for home owners and using the proven WATERMARK sensor, this simple device "controls the controller" so that watering is only allowed when necessary based on soil moisture status. One sensor and an adjustment range designed specifically for turf grass make this an affordable and simple way to make any controller with "sensor" terminals a Smart controller. 


WaterSwitch Features: 
 

• Simple to install on new or existing systems
• Easy to adjust
• Requires only one sensor
• Only allows watering if the sensing area actually requires water
• Four selectable moisture levels cover the range required for turf grass
• No need to re-program controllers for different seasons
• Pays for itself in water savings

Here's a link to some helpful and interesting Research Data.  

http://www.irrometer.com/pdf/research/Comparison_soil_matrix_potential_using_tensiometers_and_WATERMARK_sensors-Brazil_soil_erosion_paper.pdf

WATCH A VIDEO HERE