This is a device that you can keep your machine continuously charging your doorbells or thermostats. Many old homes or apartments do not have a "C" wire to their current thermostat, and newer devices require a C-wire to power the device.This simple product allows you to make the problems WIDELY USE: US power cable Powers your popular smart thermostats((Nest 1st/2nd, Ecobee, Honeywell, Sensi) and doorbells(Ring Video Doorbell, Ring Video Doorbell 2 Ring Video Doorbell Pro,Nest Skybell , etc.) and other devices that require constant AC 24 volt power for operation, enables you to charge your devices safely. EASY TO USE:Assemble along the wall from your outlet to the doorbell and thermostat without the existing doorbell or wiring. Easy installation and be able to set up in minutes. LONG CABLE:Our cable is 8M(315 inch) long and you do not worry about the distance between the socket and the Honeywell Smart Wifi Thermostat. This allows you to easily plug it into an electrical outlet inside or outside your house. SAFE AND CONVENIENT :Our battery backup has gotten certificate. A quick fix to the problem of "Low batter" you can charge it directly(plug adapter into outlet and power up). that means you don't need to remove your honeywell thermostat in order to charge up the battery.With an AC output of 24V/500mA, a perfect tool to meet your needs. WHAT YOU GET- 1. High quality accessory 2. 180 Days money-back 3 . Professional customer service. VIIVRIA has a professional team which has been specialized in designing and manufacturing transformers for years, improving technologies to meet consumers' needs.