An authentication device for fitting at the entrance to a property includes an externally facing interface including a speaker and a microphone; an internally facing interface comprising a speaker, a microphone and a keypad; and a processing unit including electrical interfaces to both the internally and externally facing interfaces and to a telephone unit. The internally facing keypad includes a button which permits a user to cause the processing unit to initiate a call using the telephone unit to a remote voice verification center via the telephone unit and the PSTN to which it is interfaced when in use (via standard telephone socket). The processing unit is additionally operable to communicate audio signals between the remote voice verification center and at least the externally facing interface (i.e. the speaker and microphone thereof), whereby a visitor may be remotely verified by the remote voice verification center before the householder grants the visitor admission to the property.