At this point, it strikes me you need a different alarm company!
Do you have a local ARRL RFI technical volunteer? You would do well
to bring them aboard, if for no other reason than to furnish third-party
testimony as to the source of interference.
Should the alarm system indeed be the source, a letter to the alarm
company detailing its lack of cooperation, your action in bringing
in a consultant, and his findings, copy to the FCC enforcement branch,
MIGHT get someone more interested in helping. I'm no lawyer, but if
I understand rightly, they have a statutory duty to stop operating
devices which cause harmful interference; their refusal could incur
the wrath of Riley.
By the way, if you want to trace noise currents without opening a line,
snap a ferrite bead around the line, and put a one turn winding through
the bead, connected to a coax to your receiver. You will in this way
be able to see which wires have more RF current on them than others.
Frankly, I doubt the noise originates in your sensors, unless they
contain processors of some kind.
If you take a short, unterminated piece of the coax center conductor,
and bring it near the alarm unit, you should be able to pick up the
electric field directly, and localize the source more precisely.
> [Original Message]
> From: Marc Ornstein <email@example.com>
> This weekend, I intend to kill the house power and disconnect the backup
> battery to make sure of this. Unfortunately, the alarm service out this
> way has been generally uncooperative on most things. As much as I would
> like to spend time trying to bypass the RFI with filters/chokes, it could
> coming from literally anywhere on any of the control lines to various
> sensors and keypads throughout the house and my time of late has been very
> limited, but I'll try maybe just at the main box itself and see what
> some chokes have an the control lines.