I think that it should be possible to design a battery that uses the saliva in someone's mouth as an electrolyte. The alerting mechanism can have correspondingly low power requirements as it could be implanted into a tooth or denture and connected electrically directly to the root. I think that such an actuator could possibly get one's attention. If a more permanent and secure solution is desired, the alterting actuator could be neurosurgically implanted directly into the brain...