Thanks, Dave. So if I just have the remote, big red button and a couple of door sensors, do I set them all to the same code, or do they all need separate codes?
What happens if my neighbor uses the same code? I have no way of knowing if they even have an X10. Will this interfere with mine?
Setting aside your security console and describing a typical X10 remote control set up: In the world of X10, you have transmitters (Palm Pad, key chain remotes, the BRB, etc.) and you have receivers that turn something ON or OFF. So lets say you have two Lamp Modules which you have plugged your two living room table lights in to. and two wall switches which each control a ceiling light fixture. Your wall switches you have set HCUC to "A2" and "A3", your two Lamp Modules controlling two table lamps in your livingroom are "A4" and "A5". I don't know which "remote" you have but pretend it is a Palm Pad and the Palm Pads RF signal is being received by a TM761 transceiver which then couples the command from the Palm Pad to the powerlines where ALL your receiver/controlling modules will receive. Your Palm Pad and the TM751 would be set to House code "A". The TM751 has a controlled outlet built in which is always #1 of what ever House Code it is set to. So buttons #2, 3, 4, and 5 on the Palm Pad will turn ON, OFF, and dim or brighten your correspondingly numbered lights. Palm Pad button #1 will switch ON or OFF the outlet in the TM751.
Can your neighbor control or interfere with your lights? Yes if they are connected to the same pole transformer as your house, OR if if they are so close that their Palm Pad (or any X10 RF transmitter) can be received by your TM751. And that is when one of you simple switches all your modules and controllers to House Code "B" or "C" or etc. etc. etc. But as Dan pointed out. X10 isn't all that popular. The odds are against your neighbor having X10.