Methods for determining an attribute of a substance in a container in response to an access event. The methods include a method for determining an attribute of a substance including activating the sensor in response to an access event and transmitting, in response to the activating, an output of the sensor providing an indication of an attribute of the contents. The methods also include a method having the steps of associating a sensor having an identifier with the container; and receiving the identifier and an output of the sensor providing an indication of the amount of the contents.