how to wire garage door into car alarm?

I want to add a quick connector to my car alarm that will plug into a home alarm system's magnetic trigger for windows and doors. the way I want it to work is when I park in the garage I can plug the door switch into the car alarms triggers but I would also like to use this when the car is out side of the garage too and since the connection could easily be unpluged I need to find a way to wire it so that unplugging it will set the alarm off. I know I will need relays but not how many and what way to wire them. I have a positive and negative trigger available on this alarm system (autopage) any ideas how I can make this happen? thanks

Well, it would obviously be easier to setup a small in home system, with a 12v inverter. Since you arent powering anything off the alarm, it wouldnt require but a couple amps to monitor all the sensors. Even an old 12v power brick could work, or a 12v car battery and a small battery tender thats designed for prolong daily use would work well. Mount the siren outside pointed down, maybe under an eave or overhang that doesnt get direct rain water. Solder the connections and you should be fine. Add as many magnetic sensors as you like and don't worry about the car to house connections. Just a thought!

bump maybe Oldspark will see this.

You do not want to use a relay.  Use the positive instant trigger.  Wire as follows.  1K ohm resistor wired to a positive voltage.  Other end of that resistor to the positive instant trigger wire of the alarm brain.  At that same point of connection, wire the normally open contact of the garage switch.  Wire the common terminal of the switch to ground.  When the switch is near the magnet, it will close the connection between the normally open contact and the common comtact.  Thus there will be ground on the positive instant trigger wire of the alarm.  When the garage door is opened, or the switch is unplugged, the 1K resistor will provide 12 volts to the trigger wire.

I don't quite understand... trip the car alarm or trip the house alarm? Why not a magnet & reed switch - reed on end of wire, magnet on the "other" end. (With appropriate resistance if used - ie, domestic alarm switch circuit should require an impedance rather than a simple open or closed loop.)

IAAI, brilliant! I think you nailed it.. I will test your idea a.s.a.p. thanks Oldspark, no home alarm involved at all, only the magnetic switch from one but I have since figured I could use a car door jamb switch if I make a simple mounting bracket. Im not familiar with a "reed" switch or if I am its not coming to me at this time. the garage is seperate from the house and I want to incorporate it into the car alarm because it should be easier than installing a new alarm system or running wires to the home alarm system. what do you think of IAAI suggestion and/or do you have a simpler one? I think his is gonna be hard to beat or make any simpler but I have yet to test it. thanks

IAAI, I was drawing your idea up on paper to get a better view for myself. so to be sure, I will need a switch in the 12v + supply line so that I can turn it off so that when the garage is not plugged in, the alarm system will still work as normal.. correct? thanks again.

I missed that noIdiot IAAI's reply, but it sounds ok. Besides, IAAI is no idiot. FYI - a reed switch is merely magnetic. Often used as window or door-open switches. 2 plastic mountings, one with a magnet, the other with the reed switch (and optional resistor). Separate the two and the reed opens else closes.

I dont have a 1k ohm resistor, I looked at all my junk too so I will see if the local radio shack has one. I also realised this woud be an easy way to incorporate a trailor into an exsisting alarm so that if it is disconnected, the alarm will go off, no? trailor thefts are way too common arround here. thanks

IAAI can confirm, but the resistor value shouldn't be too critical. Maybe 10k is ok, or higher. (The upper limit depends on the impedance of the alarm (ie, what input sensing resistors it uses); the lower resistance limit is minimise current with ignition off and the switch closed, ie, 1k is ~12mA; 10k = 1.2mA, 100k = 120uA etc.) I'd prefer higher (100k or more) to reduce current drain.