Bell 900 Series Audio Intercom System.
Each system comes with panel, power supply, electric strike and the relevant number of handsets (two button system includes two handsets/ six button system includes six handsets etc).
You can add additional handsets to the system if required (i.e if you want call button 1 to call two handsets).
Each 900 system comprises:
Model 801 series telephone(s)
Model SPA panel
Model 61 or 51 speech unit
Model 203 lock release
Model 212 or 225 power supply unit