Using Diodes in alarm installs?

I have noticed everyone talking about installing diodes inline with different parts of the alarm system and such.  But I don't understand why.  Also what kind of diodes are being installed and where can they be purchased?

most people use 1N4001 diodes, a very common rectification diode. They are used for different purposes of isolation usually, by installing a diode inline you essentially only allow current to flow one way. in crude terms you "block positive or block negative"

xetems, thanks for the quick response

So now that I know why people are useing diodes where and how do I use them.  My system is pretty simple.  I am installing the lynx 2000R aka. Airwolf.  I am going to be adding the DEI 555f i think thats the module number to get bypass PATS and I am also going to be adding a DEI 508D invisibeam. (which i don't know how to wire in) 

Diodes are made up of to parts a cathode and an anode, cathode is the side that has the gray stripe. Look at the section on this site about diodes.Gary Kline

MECP Master Technician

When electricity runs through any wire an electro magnetic field is created. When a device is turned off this field collapses and can cause some current to run in the opposite direction that it was intended. This can cause damage to the components. I use them with every wire in my installs (perhaps over kill). They can be found at radio shack with 2 in a pack for 60 cents. Part number 276-1101. 1n4001. Wire is soldered to both ends and the stripe on the diode is placed in the direction that protects the device or car brain depending on whether the circuit is positive or negative. Some local installers have stopped doing remote starters altogether. This is because they got to many complaints about the remotes causing damage to the car's ECU. (car brain)

If you are using a lot of them buy in bulk, for $88 you can get 5500 from digikey (1.6 cents each) or if you dont need that many get 100 for $3.20... I am assuming you are just saying that so people who dont use many can go pick some up, i just hate people paying those high prices at radio shack

Thanks for the help guys.... After reading the Diodes page im not sure that I fully understand everything about when where and how to place the diodes... however I am slowly but surely understanding it... The diagrams that were used are what confuses me the most. 

Xetmes thanks for the tips on where I can buy them in bulk ...and I will probably need only a few for my 1 install so unfortunatly I will be hitting up good ol radio shack .....Unless you know of some place in the northern NJ area that I can pick them up cheeper.

Yes buying in bulk is always the way to go. For the occasional user though the radio shack is well known to everyone and easy to find. I was really trying to show how commonly available diodes are. In regard to using a diode maybe some examples would help. All begins with a knowledge of the circuitry of the car your working on. Some circuits are positive. Like a brake wire circuit sends out a positive signal to the remote starter. On a typical wiring post it would look like this: BRAKE WIRE / purple + brake switch In this case the stripe on the diode would be placed toward the remote starter. This allows the brake to send a signal to the remote but blocks any stray signal from going into the brake from he remote. Why here? Well the brake switch may tie into the cruise control and eventually the car brain. So it becomes a possible place to protect. However, If the brake was sending a negative signal to the remote the stripe would be placed toward the brake.