I am adding the perimeter sensor on top of the shock sensor to the DEI Viper alarm myself. I also bought like 5 diodes the question is why is the strip side goes toward the sensor. Wouldnt that block the - output to the main unit? Why do I need to add the diodes for?

 

Unless your alarm is old you do not need diodes. You should have a multi-plex trigger input on the alarm. Anyway a diode has two sides a anode, and a cathode. Anytime a cathode is more positve than the anode no current will flow. The cathode is the side w/ the stripe. Hope this helps.