How Do Diodes Work With Hood And Door Triggers?

Please forgive my ignorance. I've spent hours reading topics online and searching through this forum and others, and haven't found an answer to my question. Possibly I just haven't looked in the right place, or put in the right search terms, but I think I've put in the time. I'm asking about the use of diodes with door and hood triggers. Everywhere I look, I see instructions to orient diodes with the banded end toward the door/hood or sensor. My understanding is that the diode blocks current flow from the banded side. In my mind, anything on the non-banded side - the alarm brain, for instance - will see nothing at the non-banded side. Like, it's a blind spot with no activity. So how is it that the alarm brain knows the ground has been disrupted when a door or hood is opened, or some other sensor is triggered? If all current coming from the banded side is blocked from flowing through the diode, it seems to me the non-banded side will present nothing at any time to the alarm brain. Probably this is a question for an electronics forum somewhere, but so many people posting here seem to have a keen understanding of electronics, so I figured I'd give it a shot since it's related to car security. Thanks!

Think of a diode as a one-way valve. So if you orient the diode with the stripe towards the negative door trigger wire and connect the other end to your alarm, the diode can supply a ground, but the alarm can't supply a ground to the car. The first few minutes of this video might help: https://www.youtube.com/watch?v=Fwj_d3uO5g8

Thank you! Very informative. Hadn't thought to look on YouTube.

Great diagram at Blocking Diodes. Not one of the electronics sites I looked at put it so simply. Feeling sheepish I never hit on the right search terms to uncover this gem. Thank you!