This device can complement a duet (base + a = satellite or 2 handsets purchased together). it is possible to run 5 in total. Shame not find pack of 3, 4 or 5. As soon as you have at least 2 handsets you can switch a call from one station to another, or to intercom. However, when you have more than 2 possible positions to make a general call (all positions together) function seems to exist in the user manual (yet quite clear and in good French) but could not make it work. you need to know which handset number the person you want to spend the communication (or an intercom message) will be able to win. Great for keys, sound, reading information ... the speaker mode, setting road .... It is a very good product for the elderly.