Abstract: A system compatible with an aperture of an asset, the apparatus for monitoring the contents of an asset, the system removable from the aperture including: a housing including a first connection interface on an exterior surface of the housing; a sensor contained within the housing; a lens contained within the housing; a power supply coupled to the sensor; an adaptor including a second connection interface configured to removably, lockably mate with the first connection interface, the adapter including a bottom end removably connectable with the aperture of the asset, wherein the aperture of the asset is substantially sealed upon insertion of the bottom end therein. A method of monitoring the contents of an asset comprising the steps of: installing an adaptor in an asset aperture; installing a sensor assembly into the adaptor; and fastening the sensor assembly to the adaptor to create a sensor apparatus.