The invention relates to a driver assistance device (2) for a vehicle (1), which driver assistance device has a radar appliance (3, 4) for determining at least one measured variable (α1, α2, R1, R2) referenced to an object (10) that is external to the vehicle, wherein the radar appliance (3, 4) comprises: at least a first and a second reception antenna (14, 15), each for receiving signals (SE1, SE2), a first down-converter (17), which is coupled to the first reception antenna (14) via a first reception path (16), and a second down-converter (23), which is coupled to the second reception antenna (15) via a second reception path (21), each for down-converting the received signals (SE1, SE2) into respective baseband signals (SB1, SB2), and a control device (5) for receiving the baseband signals (SB1, SB2) and for determining the at least one measured variable (α1, α2, R1, R2) using the baseband signals (SB1, SB2), wherein the radar appliance (3, 4) has test means (32) for producing a local check signal (SP) and for coupling same check signal (SP) into the first reception path (16) and/or into the second reception path (21), as a result of which the control device (5) receives firstly the check signal (SP) that has been down-converted by the first down-converter (17) as a first test signal (ST1) and/or secondly the check signal (SP) that has been down-converted by the second down-converter (23) as a second test signal (ST2). The invention also relates to an appropriate method.