A medical telemetry system and a method for signaling leads-off information in a medical telemetry system. The medical telemetry system according to an embodiment of the invention comprises a sensor unit comprising ECG electrodes connected to a transmitter unit, and a receiver unit connectable to ECG input connector on a patient monitor. The ECG signal and leads-off state of the electrodes are transmitted from the sensor unit to the receiver unit using radio-wave communication. Leads-off information detected by the sensor unit is transmitted to the patient monitor and signaled by feeding a predefined low-impedance DC-voltage to the ECG signal port.