Safety device for screens on a tube, particularly for technical curtains, mosquito nets, nets and roller screens, comprising: - a first spring for actuating the tube; - means (5, 6) for loading the first spring; - stopper means (15, 16, 18, 19, 20) adapted to assume: (a) a safety position, before assembling the tube in its operating position, in which they keep the first spring un-movably and safely loaded; and (b) an opening position, after assembling the tube, in which they release the first spring allowing the screen placed onto the tube to be unwound and rewound in its use positions, said safety device being further made of: - a first pin; - a supporting bushing of the tube adapted to be slidingly pushed by a small second spring on the central part of the first pin, in order to engage with its engaging teeth, antagonist teeth of a second pin; and - a dragging pin placed at the end of said first spring opposite to the end in which said safety device is inserted, said dragging pin being adapted to engage, through at least one key with which it is equipped, said tube for dragging the tube and its related screen in their use positions: whereby - said first pin is equipped with an end adapted to grip and transfer a moment to supporting devices, and made integral with the second pin characterised in that: the first spring to be held is keyed on the second pin; and - said bushing is equipped with at least one key adapted to engage the tube in order to use it for transferring the torque to the dragging pin blocking the first spring in a safety position. - a first spring for actuating the tube; - means (5, 6) for loading the first spring; - stopper means (15, 16, 18, 19, 20) adapted to assume: (a) a safety position, before assembling the tube in its operating position, in which they keep the first spring un-movably and safely loaded; and (b) an opening position, after assembling the tube, in which they release the first spring allowing the screen placed onto the tube to be unwound and rewound in its use positions, (a) a safety position, before assembling the tube in its operating position, in which they keep the first spring un-movably and safely loaded; and (b) an opening position, after assembling the tube, in which they release the first spring allowing the screen placed onto the tube to be unwound and rewound in its use positions, - a first pin; - a supporting bushing of the tube adapted to be slidingly pushed by a small second spring on the central part of the first pin, in order to engage with its engaging teeth, antagonist teeth of a second pin; and - a dragging pin placed at the end of said first spring opposite to the end in which said safety device is inserted, said dragging pin being adapted to engage, through at least one key with which it is equipped, said tube for dragging the tube and its related screen in their use positions: - said first pin is equipped with an end adapted to grip and transfer a moment to supporting devices, and made integral with the second pin characterised in that: the first spring to be held is keyed on the second pin; and - said bushing is equipped with at least one key adapted to engage the tube in order to use it for transferring the torque to the dragging pin blocking the first spring in a safety position.