Product anti-theft device, which is designed for attachment to products to be secured, in particular textile products, comprising: • a housing, and • a locking mechanism (104, 104') which comprises a needle, the needle being adjustable between a securing position, in which it engages with the product to be secured, and a release position, in which it allows detachment and removal of the product anti-theft device from the product to be secured, • the housing being of a substantially flat shape having a main plane, and • the locking mechanism (104, 104') furthermore comprising a needle receiving element which is attached to the housing and on which the needle is securely held and which is displaceable in a direction extending substantially orthogonally to the main plane of the housing, in order to transfer the needle from the securing position into the release position, and from the release position into the securing position, the needle receiving element being accommodated substantially completely in the housing, in the securing position of the needle, characterised in that the locking mechanism further comprises a locking element in the form of a slide (114, 114') which is arranged in an axially displaceable manner in the housing and which is designed in such a way that it can be brought into a releasable engagement connection with the needle receiving element, such that the needle is held securely in the securing position and that, upon actuation by a release element (118, 118') operatively connected to said slide (114, 114'), the engagement connection is released, such that a displacement of the needle receiving element and thus the transfer of the needle into the release position are permitted, the release element (118, 118') being produced at least in part from a shape memory alloy. • a housing, and • a locking mechanism (104, 104') which comprises a needle, the needle being adjustable between a securing position, in which it engages with the product to be secured, and a release position, in which it allows detachment and removal of the product anti-theft device from the product to be secured, • the housing being of a substantially flat shape having a main plane, and • the locking mechanism (104, 104') furthermore comprising a needle receiving element which is attached to the housing and on which the needle is securely held and which is displaceable in a direction extending substantially orthogonally to the main plane of the housing, in order to transfer the needle from the securing position into the release position, and from the release position into the securing position, the needle receiving element being accommodated substantially completely in the housing, in the securing position of the needle, characterised in that the locking mechanism further comprises a locking element in the form of a slide (114, 114') which is arranged in an axially displaceable manner in the housing and which is designed in such a way that it can be brought into a releasable engagement connection with the needle receiving element, such that the needle is held securely in the securing position and that, upon actuation by a release element (118, 118') operatively connected to said slide (114, 114'), the engagement connection is released, such that a displacement of the needle receiving element and thus the transfer of the needle into the release position are permitted, the release element (118, 118') being produced at least in part from a shape memory alloy.