There are many reasons that devices fail to respond. Here are the most common causes: phase loss. See the index for more information on phases and solutions.

• distance. Signals diminish as they travel along electrical wiring or through the air.
• the RR-501 transceiver "locks up" sometimes and fails to relay commands from hand-held remotes.
• the appliance module in the TM-751 transceiver is designed to not respond (sic) to X-10 commands received from the electrical wiring -- only from remotes (and the FireCracker).
• the CM-11 has been known to "lock up". It is widely believed that one cause is disconnecting the serial cable from the computer and leaving it connected to the CM-11. Always disconnect the CM-11 first. Unplugging it from the wall outlet will often solve it. Sometimes, sending "Dim" commands from another source will restore the CM-11 to normal operation.
• the device's house and unit code are not set as expected.