Car Alarms: Alarm in Toyota goes off in driveway., beep beep beep, home security system

Question
QUESTION: ALARMTEK:
I just read a response to a similar question on your list, but I am hoping for an 'idiot' proof answer.  I am not a car techie in any way!  Just moved to new home.  Driveway is slanted. MR2 Spyder by Toyota - alarm triggers while car parked at angle in driveway.  After 3 visits to Toyota, angle is NOT the problem.  BUT, I thought it was.  Now I believe it is some type of EMI or RF interference. Possible culprits are: Remote installed on home security system that allows a key-fob arm and disarm of the system or the HD DirecTV receiver dish on the roof above the garage.  
Questions: 1) Ever heard of either suspect being a trouble for alarm triggers? 2) If either of these is the problem, are there any solutions? 3)If some sort of shielding is the answer which device gets sheilded and how is it done?

Thank you SO much for your time!

ANSWER: Please describe what the alarm does when you say it's "going off". I am leaning towards it being
and after market alarm, but need your input.

ALARMTEK

---------- FOLLOW-UP ----------

QUESTION: At the Toyota dealership parts department today they said that it is a factory installed car security alarm.  Four days ago (time #2 in the shop) the techs that receive the car into the service department said it was most likely a Toyota "port installed" remote.  It was not an 'option' when I bought the car; it simply came with the alarm.  The alarm has no 'toggle' switch that allows the car to be locked without the alarm armed. Also, the car will not start unless the alarm 'ecm' is present. (and connected, I believe.)  In response to your question:  "going off" means that the alarm on the car is 'tripped' somehow and the 'somebody is trying to break in' type beep, beep, beep, beep, etc. noise continues until I press 'unlock' on the remote to disarm the alarm.  Sorry about the wordiness of this reply, but I am trying to give you all that I know.

Answer
From the sounds of it, it's aftermarket.
There may be a mercury type sensor doing htis.
Advice here then is to go to a local car alarm installation
shop, and have them locate and unplug it.

That will solve the "tilt" sensing
you are currently experiencing.

Let me know if I was right.

A.