Nothing special was planned for the day, his widow, Sue Umbers, said.
"I'm just having a quiet day."
The Maniototo policeman was bashed with his own baton when he stopped robbery suspect Richard Thomas Lakich on May 27, 1990, and he died beside his police car.
His murder shocked the close-knit town and also highlighted the vulnerability of officers in one-man stations.
Lakich, then aged 19, pleaded guilty to the murder and was sentenced to life imprisonment.
For his bravery in the execution of his duty, Senior Constable Umbers was posthumously awarded the George Medal.
Southern District police operations manager Inspector Lane Todd said no formal ceremony had been arranged to mark the anniversary.
However, a curling trophy in memory of Snr Const Umbers was contested annually by police officers and Maniototo residents.
"That's probably the occasion at which we remember Peter every year, as it's held in his honour and the trophy bears his name."
The curling match is usually held on the outdoor rink at Naseby in July, with a police team opposing a team made up of Maniototo curlers.
"It's very much a tradition. But I think the police have yet to win the trophy - there's too many good curlers on the other side."
Lakich was released on parole from prison in 2004 and lives in Kaiapoi. In a television documentary last year, he said although he was ill and would eventually need a new heart, he refused to put himself on the transplant list because he did not "deserve it".
