A method for implementing roam restriction and a system thereof are disclosed in the present invention, by setting up a list of areas where the terminal is allowed to roam. A DC output is regulated by reducing the rms value of the output voltage by twice modulating the output. The signed bundle comprises a catalog of files in the signed bundle and their associated hashes. If the first sample value is a logic 1 and the second sample value is a logic 0, this indicates that the data transmission from the security device is marginally recoverable. The substrates are additionally fastened together so that the faying surfaces compress the polyurethane sealant between them to form a fluid seal across the entire spacing between the two surfaces, and between the polyurethane sealant and the faying surfaces themselves.