Want to fit a simple alarm, wiring question

Post by **badfelafel** » Tue Jul 31, 2007 2:20 pm

Hi all... want to fit a simple siren with a keyswitch - ignition on, so will siren be, unless switch is off.

Question is: should I put the switch in the feed or the earth?

thx all!

Post by **Alec** » Wed Aug 01, 2007 9:51 pm

Hello Badfelafel,

I don't see that it will make any difference.
I presume you are taking an ignition feed to supply the siren with a switch that needs to be opened before you switch the ignition on?
A further step you could take is to install a change over relay so that if your security switch is not opened when someone switches the ignition on that the relay normally closed contact feeds the ignition coil or fuel pump (or both if you like?) That way the car is isolated as well, it is relatively easy for someone just to silence a siren by disconnecting it.

Alec

Post by **d_harris** » Wed Aug 08, 2007 12:53 am

Alec,

Picture the scene, a thief gets past the locks on an old and easy car to get into (in this case the minor) they pull out the wires from behind the igntion and start the procedure to hotwire the car. All of a sudden there is a loud siren. its going to take a very composed villian to pop the bonnet, locate the siren and then snip the wire. (even more so if its not under the bonnet!)

something like that is never going to stop someone if they really want a car (after all, you could just lift it onto the back of a loader and away you go) but it is a good method to avoid the oppertunist!

Post by **Alec** » Wed Aug 08, 2007 7:37 am

Hello Dan,

OK, but I think that it needs a little more sophistication. A simple siren that goes off if the ignition is live is also switched off by disconnecting it. At least a relay that locks itself in when activated will be more effective.
The very simple, albeit rather old fashioned, removal of the rotor arm can also be effective.

Alec

Post by **bmcecosse** » Thu Aug 09, 2007 8:20 pm

Just put a switch on the horn circuit - ignition ON and horn sounds loud and clear. Mr thief is going to run away pronto. Additional (and traditional) on a Minor is to put a hidden switch in the feed to the fuel pump. Car starts up fine - drives about 50 yds - splutters to a halt. Mr thief runs awy - the car is out of position and he isn't going to start looking for the reason why it has stopped!

Post by **Alec** » Sun Aug 12, 2007 12:29 pm

Hello BMCE,

I don't believe that a horn or siren going off attracts that much attention. Fine it it's by your house and you hear it but not a reliable theft deterrent I believe. As I said if switching on brings on a horn, switching off will stop it and any half witted person can just open the bonnet and disconnect.
The fuel cut out is far better.

Alec

Post by **Pyoor_Kate** » Mon Aug 13, 2007 8:23 am

Shall I tell you all a little story? No? Well, skip this post then...

I had a Mark 1 golf, and it had a remote alarm. All it was was a door-switch based one, but once it latched on it kept going until you pressed the button on the keyring to switch it off.

I'd noticed the range going down on the keyfob, but not got around to switching a new battery in, and I came back to my car, parked on a fairly busy sidestreet; and pressed the button; and nothing happened.

After a few goes with me standing right next to the car, and waiting for a minute before pressing it I realised it was probably dead. So I opened the car, the alarm goes off, this huge siren blaring. I open the bonnet, stick my hand in, and try the keyfob next to the alarm. Nada, the alarm's still sounding. So I lean in the car, grab my screwdrivers and proceed to disconnect the wiring from the car.

After about half a minute the battery in the siren gives out, and lo, silence returns. I shut the bonnet, hop in and drive off.

I got a couple of looks, but no one questioned me, or stopped me, and as far as I'm aware no one called the police. Certainly on my way home (less than a mile) I passed a police car and wasn't stopped.

So I now suspect that alarms do nothing against someone wanting to steal your car, but can be annoying for you.

Post by **Rob_Jennings** » Mon Aug 13, 2007 11:02 am

Quite true Kate,

best advice get a siren with battery backup and fit it inside the car, less annoying for the neighbours and pretty impossible to sit inside the car to steal it. Otherwise they are not much use

Post by **badfelafel** » Mon Aug 13, 2007 12:31 pm

i bought a dpst switch

so i think the alarm and fuel pump will run through it

its really for when the car is in the garage at home, and i will hear it if anyone tries to start it

Post by **bmcecosse** » Mon Aug 13, 2007 2:16 pm

The idea of the horn was just that it was dead simple - and scary enough to make a simple ned thief run off. The fuel pump works well - because the car is out of position when it stops - the thief is very obvious and really has no idea what has happened - and so runs off and leaves the car. Many many moons ago my Minor was taken from outside parents house - I had no idea until I walked out - NO CAR !!! - ahh there it is, 100 yds down the street! Parked, no damage. So - i'm guessing it didn't get there by itself ! And the carb was completely out of petrol.