Claire Louise Reynoldson, Nicolle Claire Mears, and Shona Dugdale, distributed keys around the island with a man’s name and phone number on.
This resulted in him getting numerous calls from people, telling him they'd found his keys.
The keys also included his work number, at the prison, which resulted in the prison switchboard getting calls.
The three women all admitted conduct amounting to harassment.
Reynoldson, aged 45, was fined £500, while the other two defendants were fined £300 each.
Prosecuting advocate Sara-Jayne Dodge told magistrates that the complainant was Reynoldson’s ex-partner.
On September 7, 2025, he received a call from a civilian telling him they’d found his key.
He hadn’t lost a key but collected it, and said that it had a plastic tag, with his name and phone numbers on, including the prison number.
He reported the matter to the police, and over the next few days received further calls, with keys found in Foxdale, Castletown, Tesco, and the Western Swimming Pool.
Ms Dodge said that 20 keys were found by the public, including at Kirby Garden Centre, the Isle of Man Airport, and in Douglas.
The man said it caused him distress and disruption.
CCTV was viewed at the Foxdale location and Reynoldson was identified and arrested.
During an interview, she admitted responsibility for distributing keys and said the relationship with her ex-partner had been toxic, and she had wanted to make his life more difficult.
She admitted dropping keys at two locations and said that the other two women had offered to take part, but none of them had realised it would be a criminal offence.
Reynoldson said the idea came from a video on social media, which said that it was a way to annoy an ex-partner without doing anything illegal.
Mears, aged 47, of Belle Vue, was interviewed and answered ‘no comment’ to questions but was shown CCTV footage of her placing a key on a bench in a play park.
In 48-year-old Dugdale’s interview, she admitted distributing three keys, saying she had agreed to assist, while at Reynoldson’s house on November 17, but said she had not known that keys had already been distributed or the extent of it.
Advocate Louise Cooil, representing Dugdale entered a basis of plea, saying her client had not been close friends with Reynoldson and had only met her once.
She said she only took three keys, putting them in a gym, the airport, and Marks and Spencer car park.
Paul Rodgers, representing Mears, also entered a basis of plea saying no harassment was intended and she had not known where the victim worked.
He said Mears was a respected professional and there'd been limited involvement, with a small number of keys.
Stephen Wood represented Reynoldson and said all the keys had been blank keys, so there had been no security issue.
Magistrates chair Julian Ashcroft said: ‘One of the main points here is don’t believe everything you see on the internet.’
Reynoldson and Mears must also pay £125 prosecution costs, while Dugdale will pay £200 costs.