a police investigation to determine the perpetrator
"detection is hard on the feet"
An act of detection.
"The new security system is excellent at detecting intruders before they can cause any damage."
present participle of detect
"The security system is detecting movement in the hallway."
In plain English: Detecting means noticing something that is there but might be hard to see at first glance.
"The security guard was detecting suspicious activity near the main entrance."