Chances are the alarm siren has died. I've replaced several.
To check, unplug the siren and connect a test light or voltmeter to the ter
minals. Unplug the hood switch, roll down the windows, and arm the alarm.
Then reach in the car and open a door, causing the alarm to activate. If
this lights the test light or produces about a 12V difference at the plug,
then the siren is the failed component.