The invention relates to a method for preventing unauthorised dialling in payphones with DTMF dialling wherein an acoustic coupler is used for dialling input. The dialling bar is achieved by disposing between the speech wires a DTMF receiver which forwards DTMF frequencies occurring on the speech wires to a telephone number bar in the dialling circuit for monitoring. Unauthorised DTMF dialling can thus at least be interrupted. The method is used in payphones with DTMF dialling.
