However, if your house has particularly old switches, or if it was renovated with switches that do not include neutral wires, you may not be able to use smart switches. (digitaltrends.com)
This isn't a problem for the average home, because neutral wires are included in the switches of most modern houses built within the last several decades. (digitaltrends.com)
Most new - ish homes (even going back to the 70s) will usually come with neutral wires in the light switch box, though. (howtogeek.com)