Low-voltage sensors and relays
Some X-10 applications require that you sense the status of a remote circuit, or control a device, but are strictly on/off in nature, and only involve relatively low voltages. Specific modules are available to meet those requirements, as listed in Table 1-6. The Universal Module lets you control devices needing a low power, low-voltage contact closure. You’ll see an application of a Universal Module in the chapter on Automated Sprinkler Control, where we’ve used one to enable or disable the 24-volt drive to the valves by a sprinkler controller.
The Powerflash does the inverse of the Universal Module, sending an X-10 message out on the power line when a contact closes or opens. You could use it to detect a switch closing and tell your PC when the garage door is open or closed; we used one in PC Toys (Wiley, 2003) as part of a system that warns you when a freezer gets too warm.