Why not just get a better speaker to replace your old one?
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As Dweller said, get the service involved. Any tampering may have a negative effect on the alarm system. If it is a private system that is not monitored, then add a headphone jack at the speaker and plug it into an amplified external speaker. Possibly a light that flashes, I have seem some audio stores that have such devices attached to phones so they observe an incoming call when demoing loud music.