Device comprising: a first node configured to receive a power supply voltage (Vcc); a second node configured to receive a reference voltage (Gnd); a first connector configured to receive a smart card, the first connector comprising: - a first electric contact connected to the first node and configured to come into contact with a first electric contact area of the card intended to receive the power supply voltage (Vcc), - a second electric contact connected to the second node and configured to come into contact with a second electric contact area of the card intended to receive the reference voltage (Gnd), and - a third electric contact configured to come into contact with a third electric contact area of the card corresponding to a three-state output; a first light-emitting diode having an anode coupled to the third contact and a cathode coupled to the second node; a second light-emitting diode having a cathode coupled to the third contact and an anode coupled to the first node; a first resistor series-connected with the first diode between the second node and the third contact; a second resistor series-connected with the second diode between the first node and the third contact; and a third resistor coupling the anode of the second diode to the cathode of the first diode, wherein the values of said resistors (R1, R2, R3) are determined so that: the first diode is on and the second diode is off when the three-state output is at the power supply voltage (Vcc); the first diode is off and the second diode is on when the three-state output is at the reference voltage (Gnd); and the first and second diodes (LED1, LED2) are off when the three-state output is in a high-impedance state. a first node configured to receive a power supply voltage (Vcc); a second node configured to receive a reference voltage (Gnd); a first connector configured to receive a smart card, the first connector comprising: - a first electric contact connected to the first node and configured to come into contact with a first electric contact area of the card intended to receive the power supply voltage (Vcc), - a second electric contact connected to the second node and configured to come into contact with a second electric contact area of the card intended to receive the reference voltage (Gnd), and - a third electric contact configured to come into contact with a third electric contact area of the card corresponding to a three-state output; - a first electric contact connected to the first node and configured to come into contact with a first electric contact area of the card intended to receive the power supply voltage (Vcc), - a second electric contact connected to the second node and configured to come into contact with a second electric contact area of the card intended to receive the reference voltage (Gnd), and - a third electric contact configured to come into contact with a third electric contact area of the card corresponding to a three-state output; a first light-emitting diode having an anode coupled to the third contact and a cathode coupled to the second node; a second light-emitting diode having a cathode coupled to the third contact and an anode coupled to the first node; a first resistor series-connected with the first diode between the second node and the third contact; a second resistor series-connected with the second diode between the first node and the third contact; and a third resistor coupling the anode of the second diode to the cathode of the first diode, wherein the values of said resistors (R1, R2, R3) are determined so that: the first diode is on and the second diode is off when the three-state output is at the power supply voltage (Vcc); the first diode is off and the second diode is on when the three-state output is at the reference voltage (Gnd); and the first and second diodes (LED1, LED2) are off when the three-state output is in a high-impedance state. the first diode is on and the second diode is off when the three-state output is at the power supply voltage (Vcc); the first diode is off and the second diode is on when the three-state output is at the reference voltage (Gnd); and the first and second diodes (LED1, LED2) are off when the three-state output is in a high-impedance state.