Lifeboat crews were scrambled after distress flares were spotted off the coast of Peterhead in the second deliberate false alarm in recent weeks.
Fraserburgh and Peterhead lifeboats were sent to Buchanhaven after several flares were spotted.
The devices, which are meant to be used to signal a vessel or person in danger while at sea, had been set off without any reason from land.
A spokesman for HM Coastguard said the people responsible had been spoken to.
Flares are sometimes used by people in the build-up to Bonfire Night instead of traditional fireworks.
This results in manpower being wasted while the emergency services search for anyone who may be in imminent danger.
The spokesman said the team had been tasked by Aberdeen’s coastguard to begin scouring the area on Friday.
“Flares are not toys or fireworks,” he added. “They are for people who may be in danger.”
Coastguard teams from Peterhead, Fraserburgh and Cruden Bay were also called to the port on September 23 in what is believed to have been a malicious act.