A method of sensing exposure to one or more of a plurality of environmental factors includes exposing a code circuit to at least some of the environmental factors, the code circuit disposed over a substrate and including a plurality of electrically-connected sensor patches, each sensor patch susceptible to one of the environmental factors, wherein the code circuit has an electrical state. An electrical excitation signal is passed through the code circuit, and a corresponding received electrical signal detected, using a transceiver formed on a transceiver substrate separate from and disposed over the substrate, wherein the transceiver includes a controller and the received electrical signal depends on the excitation signal and the electrical state of the code circuit. Using the controller, the received electrical signal or a representation thereof is automatically stored in a memory. The checking and storing steps are automatically repeated after one or more selected time intervals.