A fill detection device for a grass container includes: a detection switch; a pivot sensor that is fastened inside the grass container, that can actuate the detection switch as a result of contact with cut grass, and whose position can be changed between a raised non-detection position and a lowered detection position, the pivot sensor having: a first pressure-sensing surface that faces generally upwardly when the pivot sensor is in the non-detection position; and a second pressure-sensing surface that is linked to the first pressure-sensing surface, and that faces generally substantially rearwardly when the pivot sensor is in the non-detection position.