Designed exclusively for ecobee smart thermostats, including Premium, Enhanced, Essential, Lite, ecobee3 Lite, Smart Thermostat with voice control, and ecobee4 PEK provides an easy and cost-effective solution for homes without a common wire (C-wire). ecobee compatibility checker (on ecobee's website) helps you find out if you need a PEK Magnetic mounting ensures quick and hassle-free PEK installation on your furnace, no tools needed Scan the QR code on the box for an easy-to-follow installation guide Compatible with 24 VAC systems only, not suitable for millivolt, high voltage, dual transformer, fan coil, or communicating units All ecobee Smart Thermostats come with a Power Extender Kit in the box except Smart Thermostat Essential