The OEM process is linear and sequential: DFM design review → tooling development → prototyping and validation → testing and certification → mass production. The output of each stage is the input for the next, so any upstream change is passed down and amplified. For example, modifying the internal structure of the lock body requires re-CNC machining of the tooling, and the prototyping and certification steps must be redone as well. When evaluating lead times, buyers should factor in the number of changes and the stage at which they occur, rather than relying solely on a single figure provided by the factory.

The key to reducing risk is to clearly define requirements before changes occur. Buyers are advised to provide complete information on intended use, dimensional constraints, certification goals, and brand specifications during the DFM stage, so the factory can evaluate everything at once. After receiving samples during the prototyping stage, all items requiring modification should be listed in writing to avoid multiple small back-and-forth adjustments. For IoT smart locks that involve electronic modules, it is also recommended to agree in advance on the responsibility for firmware and hardware changes, as these directly affect the timeline for certification and mass production.