Inc. -branded modules. In response, I always ask for an exact description of the symptoms. If the symptom is that the light mysteriously comes on by itself, I also ask how long they've had the module. Invariably they've had the module many years. Early X10 modules were dark brown in color.
Later modules are light beige or white.
There are many design differences between the old and new modules. This often coincided with power line surges and sage, either from the mains or from local high-current equipment turning on or off. So, before spending a lot of time troubleshooting PLC problems consider replacing those ancient modules. Jeff also reports that, in his experience, Leviton Manufacturing Co, Inc. products experience fewer failures than X10 products. Most experts would agree, however, that products by either Leviton or X10 have far fewer failures than the obscure brands you pick up via catalogs, flea markets, and electronics shops.