Bell 900 Series Audio IntercomBell 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