An integrated activation system for an implantable medical device (IMD) sharing a power source, the activation system having a switching circuit and a sensing element coupled to the switching circuit. The switching circuit is configured to gate power from the power source to the IMD. The sensing element is configured to draw current from the power source of less than or equal to about 1 nA during inactivation, enable an operation interval of the switching circuit, and trigger a first state change in the switching circuit. The switching circuit further is configured to gate power to the IMD upon receipt of a pre-determined number of signals from the sensing element.