One way vs two way modules
The most commonly sold X10 appliance and lamp modules are one-way
modules, meaning that they listen for X10 commands and respond by
turning the device on or off, or adjusting the dimmer setting. If it
is primarily X10, and it doesn't say two way, it is probably a one way
module. Two way modules perform these functions as well, but
can also send X10 messages to tell other modules about the device
status, is it on or off, in response to an X10 status request, or when
the device status changes locally (e.g. by turing a light on or off at
the light itself). The new line of Insteon modules
from SmartHome are X10 compatible and provide two way functionaility.
One way modules are significantly less expensive than two way modules, and for most purposes you will not likely need the two-way funcionality. In fact, you don't get any benefit from a two-way modules unless you also have a controlling device that can send a status request and receive the reply, such as the CM11A , CM15A , or 1132CU computer interfaces, or or Smarthome KeypadLinc pushbutton switch. If you have a controlling device that can display device status, and the controlled device is remote, such as a recirculating pump, then the ability to monitor the status of the device makes a two-way module worthwhile.
If you do not need two-way functionaility from an X10 device, you will be better off with a one-way module. In addition to costing less, one-way modules attenuate the X10 signal less than do two way modules. Because the two way module includes a transmitter, the module will absorb more of X10 singals from other transmitters, weakening the signal available to control other devices. See the section on debugging for steps you can take to determine if this is a problem, and to correct it if it occurs.
Additional Home Automation Information