Two would-be robbers, one armed with a knife, fled a Hamilton dairy after the shopkeeper activated a fog cannon in the store.
Waikato police Senior Sergeant Phil Ruddell said the two men went into Tui Dairy on the corner of Heaphy Tce and Howden Rd about 6.30pm on Sunday.
"One [offender] had a knife and the shopkeeper has activated the fog cannon and the two have run off.
"[Fog cannons] are proving their value," he said.