Ambipolar sensors have only appeared in the past decade, i.e. very late compared to the first ambipolar electronic devices. They have been obtained with resistors, organic field-effect transistors and heterojunctions. It is not sufficient just to have ambipolar materials in order to observe ambipolar sensors. A key point is the ability to stabilize the p and n states by changing one external parameter. For further developments, it will be necessary to master a trigger that is capable of going from p-type to n-type behavior and vice versa. This can be an external bias, as in transistors, or any form of light.