The invention concerns a measurement unit including: an electric ambient energy recovery generator; an element of capacitive storage of the electric energy generated by the generator; an electric battery; a first branch coupling an output node of the generator to a first electrode of the capacitive storage element; a second branch coupling a first terminal of the battery to the first electrode of the capacitive storage element; and an active circuit capable of transmitting a radio event indicator signal each time the voltage across the capacitive storage element exceeds a first threshold, wherein, in operation, the capacitive storage element simultaneously receives a first charge current originating from the generator via the first branch and a second charge current originating from the battery via the second branch.