All I've read so far are questions about how the car owner would switch an unidentified alarm system off and on. Since you are not buying an off-the-shelf alarm what kind of alarm system are you proposing. And more importantly how will the alarm be triggered by a potential intruder.
I fondly remember back in the 1960's when my roomate bought a Honda 90 and was worried that someone might steal it. He actually did that for a couple of nights though there was no Glock available. (Provided service revolvers were locked away to prevent mischief). Quite a feat considering that we lived on the third floor of a high rise...
Like I said in another post, I don't think they're after cars, they're after wallets, electronics, etc. They've been into almost 100 cars in the last three months.
I want to hear it so I can have them meet my Louisville Slugger...
Why not just have a scr trigger from the interior light? The scr will switch the horn relay to ground. Door opens, light switch fires SCR, horn blows until someone turns off the hidden (under dashboard or seat) switch, which breaks the circuit to SCR. You could use a capacitor to give you a few seconds to leave or enter the car. After thinking about it, you may have to use a transistor to invert the signal from the door switch. You could set up your delay with the capacitor, resistor, to wait 10 or so seconds before firing the transistor, which would then set the scr. Back in the 70's when the price of gas was rocketing, people stealing gas from your car at night became a common occurance. I thought about attaching a small magnetic reed switch to the gas cap cover that would do the same thing. Just never got around to doing it. One guy I know wired a 120 volt hot wire to the frame of his car. I wouldnt recommend doing this though, it could kill someone and give you a manslaughter charge. (I know, it shouldnt be against the law to kill a thief, but it is.)
All I want is something that will blow the horn, and maybe flash the lights.
In it's simplest form, a switch mounted somewhere outside the car that turns the system 'on' by providing a ground path for a relay. When someone opens a door, the relay closes, current is passed to a flasher (like for your turn signals) and then to the horn and headlight relays. Very simple.
Also, this is instantaneous. As soon as they open the door, the horn starts. There is an 'always on' current source (courtesy lights) that do not turn off when the dome light is turned off, so I intend to use this for the 'trigger'.
looks to me like you have it all figured out. So why are you asking us this? You know you could give away your secret device. For instance, from this conversation thus far, if I were a crook, I would know to look under the fender of your car for a keyswitch. Then take a sharp chisel and hammer and shear the switch off, then cut the wires to the switch, then get on with business as usual. Sometimes the best intrusion device is to catch the crook offguard. I kinda like the string tied to the toe suggestion. Ive heard it works for napping while fishing too.
One of the reasons I left. (I used to live in RI).
Biggest complaint: Idiotic handgun policies for law abiding citizens.
Biggest hassle: High taxes and auto insurance rates
Biggest disappointment: Them thar' politicos keep on makin' the same mistakes and the dumb public keep on electin' 'em!
Oh, and don't forget the copious amount of salt/chemicals used to de-ice the roads and eat away on our cars. Which brings us to COLD winters that are far too long.
Other than that, it's beautiful country...
JT
(It might be hot in the summer in TX, but that's why gawd invented A/C)
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