The Simplex 4098-9794 is a modular TrueAlarm sensor base with built-in electronic alarm sounder.  The Piezoelectric sounder provides high output (88 dBA) with low current requirements (20 mA) and is interchangeable with TrueAlarm sensors; photoelectric, heat or ionization (ordered separately).  The 4098-9794 sounder bases are for use with Simplex® control panels model 4010, 4020, 4100, 4100U, 4120, and Universal Transponders.