The police have warned that burglars are on the prowl and leave small pieces of cardboard behind at front doors. These pieces of cardboard have been observed in Noord-Eindhoven.
It is a well-known method of burglars to determine if there is someone home. The piece of cardboard is wedged between the front door and frame. Later the criminals will return to see if it is still there. If the piece of cardboard has fallen to the ground, the door has been opened and there is someone home. If not, they strike.
A police officer from Vaartbroek put a photo of a piece of cardboard used, on Twitter.