It’s possible that there could be a few reasons why your Gentex S1209F is not sounding properly during testing. Firstly, ensure that the unit is receiving power by checking the connections and ensuring there’s no power outage. Additionally, verify that the alarm is properly installed according to the manufacturer’s instructions, including proper placement and mounting. If these basic checks don’t resolve the issue, it could be a malfunction within the alarm itself, and you may need to contact Gentex customer support or consider replacing the unit.