With time, I gathered some rules:
- don't put a motion sensor (MS10) nearby a halogen lamp: if that lamp was used just before leaving the house, the residual heat will be detected and trigger the alarm.
- don't stick the door sensor (DS10) directly onto an aluminum door frame, it may prevent it from working. Put a plastic or wood block between the frame and the magnet.
- don't leave some kitchen appliance (a certain "Rocket Blender" in particular) plugged even when not in use: the noise generated will stop the propagation of the X10 signal .
- beware of some surge protected power strips: they can suppress the signal just like the kitchen appliance above.
- a computer power unit with noise filter may absorb the X10 signal. A X10 filter (FM10) may be needed in this case and the 2 others before. (see this excellent article on noise and signal absorption)
- don't use the X10 Lamp Dimmer (LW10) with any Energy Saving CFL (even the new dimmable ones) , you may fry either or both. Use AW10 instead when in doubt.
- If you just added a MS13 wireless PIR and some X10 lights or appliances turn on or off with no apparent reason, remember that the MS13 control also the device number just over the one you setup (U+1). This one will be subject to the Day/Night detection.
- don't think that, because you're the only one to have an X10 alarm central in the vicinity, that it will not get interferences from other wireless alarm systems. Mine was going off every day at 3:30PM, which corresponded to when a neighbour returned home and disarmed his alarm: an cheap unbranded wireless model. The solution was to change the home code of mine.
You would also discover that these systems are packet with all sorts of bugs and, since their firmware can't be updated, you end up buying a new central unit every year or so:
Marmitek SC2700: no support for thermostat sensor
Marmitek SC2770: some support for thermostat sensor with bugs (Digimax 210)
Marmitek SC2800: better support for Digimax
SC9000: support for Digimax (although a first batch sold didn't support it).
New casing with LCD display for easier programming. X10 events scheduler.
SC28 (also called SC9100 and HomeProtector+): scheduler can control the Digimax thermostat, so you can set a lower temperature at night. Less bugs but the PS18 power supply can be problematic (mine blocked all X10 signal at some stage and had to be replaced)
The most annoying in the X10 world is the complete lack of communication and support from the manufacturers, to a point where the resellers themselves are often confused and sometimes advertise features that are not part of the model they have in stock.
A precious source of information is the AutomatedHome.com support forum.
All in one, I love and I hate X10 automation. Those who have such an equipment will understand what I mean. The central units discussed here are entry level (around €90 for the central unit alone), Some more expensive and reliable wireless alarm systems are now available, but they probably still don't beat a wired alarm system for the reliability.