A method for protecting a secured real time clock module, the method includes: locking multiple input ports of the secured real time clock module if the multiple input ports of the secured real time clock module are idle during at least a first duration; unlocking the multiple input ports of the secured real time clock module if a predefined high frequency code is received over a control input port of the secured real time clock module; and providing a secured real time clock signal when the multiple input ports of the secured real time clock module are locked and when the multiple input ports of the secured real time clock module are unlocked; wherein changes in a supply voltage results in a supply voltage induced changes of an input signal provided to an input port of the secured real time clock module; wherein a maximal frequency of the supply voltage induced changes of the input signal is lower than the high frequency of the predefined high frequency code.