X10 PRO SMART COUPLER / REPEATER FOR USE IN ALL X10 PRO INSTALLATION For professional, reliable systems, phase coupler/repeaters are recommended for every X10 PRO installation. Note: Installation must be carried out by qualified installers only. Installs at the electrical panel to couple, amplify and repeat X-10 command signals. Boosts the X10 signal to 5-7 Volts. Recommended in situations where the residence is over 2,000 square feet and/or the transformer feeding power to the house is over 100 feet away.