An implant capable of sensing pressure, force, pH level or any other condition releases a chemical into the body when a pre-set limit is exceeded. The chemical is chosen to be detectable by the person without the need of any external equipment. Typical chemicals are dyes causing coloration visible to the person or chemicals causing a mild and clearly identified reaction such as odor, taste, or unique sensation. The released chemical can have therapeutic effects as well. The invention is particularly suitable for detection of abnormal increase of internal pressure in order to monitor stent grafts.