Hardwired power supply for siren

Hello community, Yesterday I connected the Rind Siren with built in batteries and additional 12V power supply. The Ring app didn’t show the Siren hardwired connected ( it says batteries are ok). Next I checked the voltage across the terminals and it surprisingly had dropped to 1.5v. When disconnected the power supply shows correct 12V. Can you please help what might be happening here? Thanks