To find the appropriate alarm model for an application, just find where the sound level needed and the voltage required intersect on the chart. The example here shows that for an application requiring a medium sound level along with a voltage range of 28 to 48V AC or DC, the model number needed is SCE048MA3CTB. Please note that only the part numbers highlighted in the selection guide are currently stocked by DigiKey. All of the other part numbers can be ordered through DigiKey as Non-Catalog items.