The On Detection setting in the Detection menu defines whether the decoder should beep and / or blink to signal a detection.
Note that there is a limit to the frequency of the beeps and blinks, these are only queued for 2 seconds. If too many athletes are being detected at the same time, the system will not be able to beep and blink for every athlete, and you would not be able to make out every separate signal anyway.
If the density of athletes crossing the timing system is low, the system will signal every detection separately with a short delay so that you can verify the number of detections easily.