Sensor is the device that detects a physical, chemical, or biological signal. In medical diagnostics, sensors detect heart signals (ECG), brain signals (EEG), muscle signals (EMG), temperature, pressure, oxygen saturation, etc.
Example:
ECG electrodes detecting ionic currents.
Pulse oximeter’s photodiode detecting oxygen saturation.
Importance: Without a sensor, there would be no way to capture the signal from the human body.
Transducer converts one form of energy into another. In diagnostics, it usually converts biological/ionic signals into electrical signals that can be amplified and analyzed.
Example:
ECG electrode is also a transducer (converts ionic currents → electrical current).
Ultrasound transducer (piezoelectric crystal) converts electrical energy → sound waves → back to electrical signals.
Importance: Without a transducer, the captured signal cannot be processed, displayed, or stored.
Which is Most Important?
- Sensors are the first step they detect the signal (heart, brain, muscle, etc.)
- Transducers are the bridge they make that signal usable by the machine.
Many devices (like electrodes in ECG/EEG/EMG) act as both sensor and transducer at the same time. In diagnostics, both are equally important the sensor ensures we capture the right signal, and the transducer ensures we can interpret it.
The unsung heroes of medical diagnostics are sensors and transducers. Transducers transform vital physiological signals from sensors into electrical data that can be used for analysis. Devices like pulse oximeters, ECGs, and EEGs couldn’t work without either. Both functions are deftly combined in many contemporary devices, resulting in precise and effective diagnostics. They serve as the foundation for accurate, real-time patient monitoring and medical decision-making. 
