The protocol may transmit a message that says "select code A3", followed by "turn on", which commands unit "A3" to turn on its device. Several units can be addressed before giving the command, allowing a command to affect several units simultaneously. For example, "select A3", "select A15", "select A4", and finally, "turn on", causes units A3, A4, and A15 to all turn on.

There is no restriction that prevents using more than one house code within a single house. The "all lights on" command and "all units off" commands will only affect a single house code, so an installation using multiple house codes effectively has the devices divided into separate zones.

List of X10 commands

Code	Function	Description	One Way	Two Way
0 0 0 0	All units off	Switch off all devices with the house code indicated in the message	X
0 0 0 1	All lights on	Switches on all lighting devices (with the ability to control brightness)	X
0 1 1 0	All lights off	Switches off all lighting devices	X
0 0 1 0	On	Switches on a device	X
0 0 1 1	Off	Switches off a device	X
0 1 0 0	Dim	Reduces the light intensity	X
0 1 0 1	Bright	Increases the light intensity	X
0 1 1 1	Extended code	Extension code		X
1 0 0 0	Hail request	Requests a response from the device(s) with the house code indicated in the message		X
1 0 0 1	Hail acknowledge	Response to the previous command		X
1 0 1 0	Pre-set dim	Allows the selection of two predefined levels of light intensity		X
1 1 0 1	Status is on	Response to the Status Request indicating that the device is switched on		X
1 1 1 0	Status is off	Response indicating that the device is switched off		X
1 1 1 1	Status request	Request requiring the status of a device		X

With 60 Hz AC current flow, a bit value of one is represented by a 1 millisecond burst of 120 kHz at the zero crossing point (nominally 0°, but within 200 microseconds of the zero crossing point), immediately followed by the absence of a pulse.
A zero value is represented by the absence of 120 kHz at the zero crossing point (pulse), immediately followed by the presence of a pulse.

All messages are sent twice to reduce false signaling. After allowing for retransmission, line control, etc., data rates are around 20 bit/s, making X10 data transmission so slow that the technology is confined to turning devices on and off or other very simple operations.

In order to provide a predictable start point, every data frame transmitted always begin with a start code of 1110.
Immediately after the start code, a house code (A-P) appears, and after the letter code comes a function code.
Function codes may specify a unit number code (1-16) or a command code, the selection between the two modes being determined by the last bit where 0=unit number and 1=command. One start code, one letter code, and one function code is known as an X10 frame and represent the minimum components of a valid X10 data packet.

Each frame is sent twice in succession to make sure the receivers understand it over any power line noise for purposes of redundancy, reliability, and to accommodate line repeaters.