question about the microcontroller in my car alarm

[Andrew MacGinitie]

i bought a used toyota with a factory installed car alarm, which is as
evil as all noisy car alarms, i.e., it goes off randomly, frequently,
for no apparent reason. since it is activated by locking all the doors,
i can prevent its activation by leaving at least one door unlocked.

how might i go about tricking the alarm into thinking one of the doors
is unlocked, when it's actually locked? thereby allowing me to lock all
the doors w/o activating the alarm. i know how to use a multimeter, but
i'm not sure what or where to test. would i have to disassemble a door?
(i hope not)

so far i've complained about the problem to 2 different toyota
dealerships, and they've both told me they can't disable the alarm;
otherwise i'd be happy to pay them to do it... well, ok, not happy,
let's say willing. i assume there's a microcontroller involved in
reading door lock and other sensor statuses, and controlling the alarm.
(the alarm is the kind that honks the horn & blinks the headlights, in
case that's relevant.)

[Colin Willson]

All you most likely have to do is ground one of the door sensing wires. Does your car have a trunk? That would be the easiest one to get to. The sensor wire is usually just wired to the light so when you open your trunk and the light is grounded to turn it on, it grounds your alarm sensor wire as well. If you can find that, you could just pull it off the light and permanently ground it to the car body.

Otherwise, Do you know where the alarm unit is? If you can get to it, you'd have to figure out which wires go to the door locks. Usually the wires go into the alarm unit in a big plug which you can pull off. Test each connection by using a multi meter and just check for continuity to the metal car body (unpainted bolts, ect..) while triggering the locks. If you figure it out, just snip the wire or permanently ground it depending on whether the circuit is open or closed while unlocked (I can't remember what it is usually).

If you know the alarm model, you might be able to find the install manual online which would have the color codes for the different wires coming out of the alarm which would make your life even easier.

I haven't installed an alarm in years.. I moved to NY to get away from my car..

Hope that helps!

--Colin Willson

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[Pablo Echegorri]

theres also another issue if you do manage to trick the car into
thinking one of the doors in unlocked the lights inside the car might
stay on and kill the battery.
otherwise just find the horn somewhere inside the hood and unplug it.