This 2 in 1 combo comes with 24vdc hooter and manual callpoint in MS enclosure.this is 4 wire system.Sounders areaudio notification device used alert trained personnel toinvestigate possible emergency situations and to takeappropriate action during fire detection. AAS-HMCH-MS ismade of MS sheet with powder coated finish and isapplicable for indoor use only. and come with a factory fittedback box for surtace mounting or semi-flush mounting.