dei ground when armed starter kill

Okay, question: Why did DEI program their alarms to send power to a starter kill relay when the system is armed? Wouldn't this cause significant battery drain after some time with a relay constantly being active?

Wouldn't it of been better to use a N-O relay instead, and have the alarm module apply power to the relay when the system was disarmed instead, closing the starter circuit, and allowing the car to start?

You are completely wrong,  that relay will only draw power  when the alarm is ON and a hotwire attempt is made,  if you don't understand that you should read up on relays.  Armed output goes to 85 on the coil, ign goes to 86 on the coil, thus coil will only be energised and  drawing power if BOTH the alarm  AND the ignition were on at the same time.

DEI was "smart" about it - they designed it to be "fail safe".  The last thing a large alarm company wants is to be blamed for leaving customers stranded if the alarm fails.

In your scenario, if the main alarm fuse blew, or the alarm failed, the car wouldn't be operable.  Using the NC contact means that you can actually remove the alarm brain and the car will still start (as long as you don't cut the starter kill wires).

In the end, if you think about it, a starter kill, no matter how you do it, isn't really that secure.  If someone is able to access the wires to hot wire the car bypassing a simply relay isn't really a challange!

Ahhh...I see what you mean. The coil will only be active if the alarm is armed and it sees current from the IGN switch? Well, that's pretty clever then! I was looking at the DEI relay, and there is only 3 wires, so this makes sense...

However, if someone is trying to steal your car, it makes it a little easy for them to locate the starter kill relay...they just need to listen to the clicks whenever they turn the IGN :)