Abstract: An apparatus for measuring the distance between a first sensor and a surface in a refuse container is disclosed. The apparatus includes a first transmitter, the first transmitter configured to transmit a first electromagnetic signal toward a set of surfaces at a first time; and, a first receiver coupled to the first transmitter, the first receiver configured to receive a first reflected electromagnetic signal from the set of surfaces at a second time. The apparatus further includes a distance calculating circuit coupled to the first receiver, the distance calculating circuit configured to calculate a first flight time period between the first time and the second time. The apparatus also includes a time-distance conversion circuit coupled to the distance calculating circuit, the time-distance conversion circuit configured to convert the first flight time period to a first distance; wherein a notification is generated if the first distance is less than a first threshold distance.