Google GVNZ4 Nest Power Connector 
C-wire substitute for Nest Thermostats
Works with the Nest Thermostat, Nest Thermostat E and 3rd gen Nest Learning Thermostat
Please note, this works with 24 VAC systems ONLY. Millivolt and high-voltage systems are incompatible
Sealed in package 
In brand new condition 
See pictures for details