How can I test to see if a diode is dead or alive?

 

use a multimeter set it on the diode setting. Put the red lead on the diode side with the bar the negative lead on the other side it shout say around .7

If your multimeter does not have this feature use the impedence setting. measure in both directions one of the ways should have a significantly lower resistance.

Either of these test does not garantee the diode is good. What are you using it for?

 

I'm using it to isolate sensors, door locks/unlocks, door triggers and probably a few other things to install my alarm. I will try what you said tonight.