Any device that receives a signal or stimulus (as heat or pressure or light or motion etc.) and responds to it in a distinctive manner(noun)
WordNet. Princeton University. 2010.
Use "sensing element" in a sentence
"Instead, the sensing element comprises an array of microscopic 10µm diameter copper capacitors located behind a durable pure glass panel, which completely protects the sensor from any day-to-day wear and tear, as well as moisture and dirt."