Smart devices are ubiquitous in modern environments, yet their decommissioning phase remains poorly studied and often overlooked in system design. We define secure decommissioning as the process by which a smart device securely disconnects from its environment and makes sensitive data inaccessible. If not decommissioned, devices may retain sensitive information — such as security credentials or user-behavior data that could be recovered by an adversary. Unfortunately, some users may forget to decommission a device when they dispose or sell it, and cannot decommission a device that is lost or stolen. This paper investigates a trigger mechanism for individual wireless smart devices to automatically identify conditions requiring decommissioning. Our approach does not require any hardware changes to wireless devices. We evaluated it through extensive simulations and validated it on real IoT-class hardware. With appropriate parameter values, our mechanism always correctly identified when to decommission and never falsely decommissioned. These parameters can be tuned to user needs.