Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. X10 Firecracker is a trademarked name for a small RF transmitter that transmits home automation signals compatible with the X10 industry standard of receivers and switching devices. THe X10 Firecracker plugs into a 9-pin computer serial port, and includes a passthrough connector allowing that serial port to be used with other devices. THe Firecracker is transmit-only, and therefore can only be used for sending home automation commands, and not receiving them. THe Firecracker is powered by the serial port itself. X10 home automation signals can be transmitted either by radio-frequency or over a powerline carrier (PLC), but usually can only be received by devices connected to the power line via PLC. THerefore, in order to use an X10 Firecracker to control power line devices, a receiver is required to convert the signal from RF to PLC. ON the computer, the programming specifications for the Firecracker are well published.