The invention relates to a cash box (10) having a receiving area (12) for receiving notes of value, an invalidating unit (14), a sensor unit (18) for detecting manipulation attempts and a control unit (16). In an activated operating state, the control unit (16) triggers the invalidating unit (14) when the sensor unit (18) detects a manipulation attempt. In a deactivated operating state, the control unit (16) does not trigger the invalidating unit (14) even in the presence of a manipulation attempt. Prior to the activation of the cash box (10), the control unit (16) checks the proper functioning of at least one sensor (20) of the sensor unit (18). In addition, the invention relates to a method for activating a cash box (10).