Pro1IAQ Model Wireless Wire  - The WW160W "Wireless Wire" functionally replaces 24V thermostat wiring. 

Great for many applications - use instead of running wires when you need to:

• Make any thermostat wireless (up to 2H/2C Conventional or 3H/2C heat pump)
• Add wires to condensing unit
• Add wires when upgrading to multistage system
• Add wires anywhere wiring is difficult

To use the wireless wire- simply connect the terminals on one module and when those terminals see 24V - the same terminals on the other module closes.    You must have 24VAC power for both modules. 
Module dimensions approximately 4.25" H X 4.5" W X 1-1/8" D.  Wireless Wire includes one input module and one output module.