Some embodiments include observable properties triggered upon interrogation of RFIDs. The RFIDs can be passive RFIDs, and the observable properties can be visible changes that require little power to generate, and little or no power to maintain. The visible information can include information about items tracked with the RFIDs, such as shipping information. Some embodiments include passive RFIDs utilizing a single antenna to power an integrated-circuit chip and a visual identifier. Some embodiments include methods of locating interrogated RFIDs. Some embodiments include methods of tracking items.