A wake-up mechanism for a mechanical timepiece comprising: - a striking mechanism; - a motor-spring arranged to unwind while driving the striking mechanism following triggering of the latter; - a trigger system comprising a trigger cam arranged to be connected to the hour wheel of the movement by a first gear train so as to be driven in rotation, in a given direction, around an axis at a rate of one revolution in twelve or twenty-four hours, and arranged to command triggering of the striking mechanism when it reaches a predefined angular position; - a display arranged to indicate a programmed wake-up time at which the trigger cam should command triggering of the striking mechanism, after having traveled the angular distance separating a current angular position from the predefined angular position; - a setting system for setting the programmed wake-up time comprising a control member that can be actuated manually and arranged to control the display, the setting system also comprising a second gear train arranged to connect the display to the trigger cam, so that the wake-up time setting system allows the current angular position of the trigger cam to be modified, while shifting the programmed wake-up time indicated by the display, the second gear train being arranged so that the hour wheel does not change the display when it drives the trigger cam; - the first and the second gear train comprising a common part directly upstream of the trigger cam, and the gears of the common part having a cumulative transmission play capable of giving the trigger cam an angular play sufficient to give rise to a substantial offset between the programmed wake-up time and the time at which the trigger cam reaches the predefined angular position; - characterized in that the mechanism comprises a play take-up cam fixed coaxially to the trigger cam, and a roller or an inclined surface biased against the profile of the play take-up cam by the return force of a spring, the play-take-up cam, on the one hand, and the roller or inclined surface, on the other hand, being arranged to cooperate so that the force exerted by the roller or the inclined surface on the play take-up cam generates a torque capable of causing the latter to pivot, and - in that the profile of the play take-up cam is such that, when the modulus of the angle which separates the current angular position of the release cam from the predefined position is less than or equal to the cumulative transmission play, the generated torque is oriented in the opposite direction to the given direction and it is strong enough to tension the gears in the common part that is part of both the first and the second gear train. - a striking mechanism; - a motor-spring arranged to unwind while driving the striking mechanism following triggering of the latter; - a trigger system comprising a trigger cam arranged to be connected to the hour wheel of the movement by a first gear train so as to be driven in rotation, in a given direction, around an axis at a rate of one revolution in twelve or twenty-four hours, and arranged to command triggering of the striking mechanism when it reaches a predefined angular position; - a display arranged to indicate a programmed wake-up time at which the trigger cam should command triggering of the striking mechanism, after having traveled the angular distance separating a current angular position from the predefined angular position; - a setting system for setting the programmed wake-up time comprising a control member that can be actuated manually and arranged to control the display, the setting system also comprising a second gear train arranged to connect the display to the trigger cam, so that the wake-up time setting system allows the current angular position of the trigger cam to be modified, while shifting the programmed wake-up time indicated by the display, the second gear train being arranged so that the hour wheel does not change the display when it drives the trigger cam; - the first and the second gear train comprising a common part directly upstream of the trigger cam, and the gears of the common part having a cumulative transmission play capable of giving the trigger cam an angular play sufficient to give rise to a substantial offset between the programmed wake-up time and the time at which the trigger cam reaches the predefined angular position; - characterized in that the mechanism comprises a play take-up cam fixed coaxially to the trigger cam, and a roller or an inclined surface biased against the profile of the play take-up cam by the return force of a spring, the play-take-up cam, on the one hand, and the roller or inclined surface, on the other hand, being arranged to cooperate so that the force exerted by the roller or the inclined surface on the play take-up cam generates a torque capable of causing the latter to pivot, and - in that the profile of the play take-up cam is such that, when the modulus of the angle which separates the current angular position of the release cam from the predefined position is less than or equal to the cumulative transmission play, the generated torque is oriented in the opposite direction to the given direction and it is strong enough to tension the gears in the common part that is part of both the first and the second gear train.