Word to the wise.  When buying a home intercom system, it is most advisable that you buy only those that are featured as WIRELESS.  To purchase any other intercom system that is not wireless you will more than likely be limited to use the units only if there are plugged into the same circuit.  This means that you will not be able to place the units any where in the home because the circuitry for each room will vary depending on your home.  It should be also noted that non-wireless intecom system (i.e Westinghouse) require that the units be plugged directly in the home outlet.  Units will not operate if plugged into a adapter, surge protector, etc.  Good luck with your purchase, hope this helps for anyone thinking to buy a home intercom system.