This is the 11343rd most frequent Russian word.
детектором
The Russian word "детектором" means "detector" (instrument or device for detecting something).
The word 'детектором' (detector) is used in the instrumental case to indicate the means by which something is accomplished, referring to the device detecting lies.
Этот прибор работает как детектором лжи.
This device functions as a lie detector.
Here, 'детектором' is in instrumental case and denotes a tool or device utilized for an action — detecting motion.
Мы воспользовались детектором движения для обеспечения безопасности.
We used a motion detector for security purposes.
In this sentence, 'детектором' is instrumental case, showing interest in a specific type of device related to radiation detection.