A mechanism for ensuring the physical location of data processing devices as a security check is provided. With this mechanism, security data is transmitted to data processing devices via an electrical network and is used to perform a security check to determine if the data processing device may operate. The data processing devices may be limited such that they may only power-up, boot-up, or remain operational when they are coupled to the electrical network. Thus, they must be physically located such that they may gain access to the electrical network. In addition, a security check may be used to control which data processing devices may communicate data packets with one another over the data network. When a data packet is received by a data processing device, security data in the data packet is compared against a local history of security data received by the recipient of the data packet via the electrical network. If matching security data is found in the history for the same time represented by an associated timestamp, then the sending data processing device and the receiving data processing device are determined to be present on the same electrical network and may communicate with one another.