The present invention relates to an anti-intrusion device for the protection of housings. It applies in particular to the protection of a housing of an electronic payment terminal or of a housing for entering a confidential code (also known as a “PIN-pad”).The anti-intrusion device according to the invention makes it possible to detect any attempts to open a housing. It comprises at least one spring (3), the spring being arranged in such a way as to be under pressure and to act electrically on an electronic circuit (2) when the housing is closed, and to no longer act on the electronic circuit when the housing is open.