The monster, or Geoff, is approaching the city. You would need to use the audio and video system at the field to attracts its attention.
This is the low-spoiler guide for "Signaling the monster" puzzle in The Darkside Detective - A Fumble in the Dark. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.