Householders with cat flaps are being warned to be on their guard against burglars.
Thieves are reaching through the flaps to hook car and house keys left in locks or near doors.
There has been a series of cat flap burglaries in Nottinghamshire, including one at Eastern Avenue, Newark.
They all happened overnight, with jewellery and electrical items taken.
The offence at Eastern Avenue was on September 18/19 when a thief reached through a cat flap for a set of keys and used them to gain entry to steal electrical items.
Inspector Louise Clarke, of Newark Police, said if cats were kept in at night or householders were away then a lock or bolt should be used to secure the cat flap.
Inspector Clarke said keys should not be left in locks or in range of a hooked implement that could be used to retrieve them through a cat flap.
“Quite often people will think it’s enough to ensure that a door is locked but, as these offences prove, keys should always be kept far from reach,” she said.
“Because they feel their property is securely locked when they go to bed, a householder may not immediately realise their property has been entered or how it was entered, and that their personal items are even missing.”
Inspector Clarke said vehicles should be left in garages if possible, in case vehicle keys were targeted.
Suspicious activity should be reported on 101. In an emergency, or where a crime is in progress, call 999.
Police are also investigating a number of thefts of tools from vans.
Thieves have targeted vans in Newark, Muskham, Sutton-on-Trent and Edwinstowe.
Similar offences have been reported in Worksop and Retford, but it is not known if they are linked.
Inspector Clarke said: “Tools are being targeted.
“It might seem a bind to remove tools from a van every night, but if you are a tradesman and rely on two or three tools for your livelihood on a daily basis, and they are the most expensive ones, take them out at night because the cost of replacing them and the loss of earnings is far more of an inconvenience.
“Wherever possible, park a van under a CCTV camera or street light and put additional locks on a vehicle.”