You ask...
So If I was replace the 16 speaker I have currently and buy an elmdene 8 ohm speaker will I get a louder alarm volume or will it not make a difference? Thanks
No you will not get a louder volume - you will get less sound.
The output impedance and the speaker impedance should match - notice the guidance calls for a 16 ohm speaker.
I know noting about alarm systems - I know very little about impedance matching of speakers but enough to warn you to abandon your plan.
Good Luck...
December 2015