People were stunned as envelopes stuffed with £100 cash were posted through letterboxes on Christmas Eve with a note saying it was a 'random act of kindness'.
Multiple residents in Clifton in Nottingham reported receiving the random envelopes with a cool hundred inside the night before the big day.
One neighbour said they were "overwhelmed" with the gesture while another was left "crying" thinking the unidentified donor must have a "heart of gold".
One family even heard a knock at the door before find the envelope - but the mysterious gift-giver was nowhere to be seen by the time they answered.
Speaking to NottinghamshireLive, 41-year-old Emily Crane said she was at home with her family yesterday afternoon, when the secret Santa came a knocking.
Emily said: "There was a knock on the door, my son went to answer the door.
"There was an envelope on the floor.
"He looked outside and did not see anybody, I got an envelope which said 'Random Act of Kindness' and some money inside."
The mum-of-two described the gesture as "very overwhelming" and said whoever had posted the money had a "heart of gold".
The childminder, of Peacock Crescent, added: "Clifton has got a great community spirit anyway, people like this are worth their weight in gold," she added.
Later, she and her family used some of the dosh to help fund a trip to National Trust attraction, Belton House country estate and deer park, in Grantham.
Cherie Haynes, 38, who lives in nearby Rivergreen, also described feeling overwhelmed by the heartwarming gesture.
She said "we just heard the letterbox go" and added she thought "it's probably one of those free newspapers".
One of her sons found their envelope on a doormat.
Ms Haynes said: "I realised it was a Random Act of Kindness envelope, so I opened it with no major expectations.
"There was £100. It just set me off crying. It's really uplifted the whole morale of the house.
"I have no idea whatsoever [who delivered the letter].
"It would be nice to be able to thank them personally.
Each envelope contained the same note saying it was a message saying simply it was a 'random act of kindness'.
