Police have written to licensees in Norfolk to warn them about a gang of thieves who are targeting pubs in the area.
In the last month, four pubs have been broken into when they were quiet or closed, and the burglars have escaped with more than £3,000 in cash and cigarettes.
Det Insp Steve Strong, who is heading the investigation, said: "We are warning licensees to be aware of strangers visiting their pubs and people taking an interest in what's happening with the takings."
He is writing to advise publicans to lock takings away in a safe, if possible, or otherwise take the money through with them to their private quarters after locking up.
The most recent break-in was at the Three Pigs pub at Edgefield, near Holt, when £1,280 was taken from the till.
In another incident, three men with London accents escaped empty-handed after trying to steal cash from a till at the King's Head in North Elmham, near Dereham.
They caused more than £350 of damage, but left after being disturbed.
The Globe on the Buttlands at Wells was targeted by thieves who took £1,400 in four cloth bags.
Then, on April 1, a pub in the North Walsham area was robbed of cash and cigarettes to the value of £380.
Det Insp Strong said: "It would appear that the offenders are targeting pubs in the afternoons when trade is slow or when the premises are closed and the owners are in areas away from the bar."
Anyone with information relating to any of these offences is asked to contact Det Insp Strong at North Walsham police on 01953 424242.