FIELD: telephone communication. SUBSTANCE: invention refers to telephone installation to send information over telephone line that includes telephone set manufactured in correspondence with version without subscriber's payment and switched into mentioned telephone line and test module bridged to telephone line and connected to telephone set. Telephone set transmits certain elements of information ((K1
i
)) prepared in advance in accordance with some algorithm with use of random number and number of called telephone set at certain time moments determined beforehand. Module generates elements of information Ki on basis of same algorithm and same random number and compares them with elements of information K1
i
. Module initiates disconnection circuit when compared values do not agree. EFFECT: protection against intruders. 11 cl, 3 dwg
